diff --git a/frontend/src/services/investments.ts b/frontend/src/services/investments.ts
index 9d978a9..74921d6 100644
--- a/frontend/src/services/investments.ts
+++ b/frontend/src/services/investments.ts
@@ -1,5 +1,5 @@
 import api from './api'
-import type { InvestmentHolding, InvestmentPerformance } from '@/types'
+import type { InvestmentHolding, InvestmentPerformance, CreateInvestmentHoldingRequest, UpdateInvestmentHoldingRequest } from '@/types'
 
 export const investmentsApi = {
   getHoldings: (accountId: string) =>
@@ -7,4 +7,13 @@ export const investmentsApi = {
 
   getPerformance: (accountId: string) =>
     api.get<InvestmentPerformance>(`/investments/${accountId}/performance`),
+
+  createHolding: (accountId: string, data: CreateInvestmentHoldingRequest) =>
+    api.post<InvestmentHolding>(`/investments/${accountId}/holdings`, data),
+
+  updateHolding: (accountId: string, holdingId: string, data: UpdateInvestmentHoldingRequest) =>
+    api.put<InvestmentHolding>(`/investments/${accountId}/holdings/${holdingId}`, data),
+
+  deleteHolding: (accountId: string, holdingId: string) =>
+    api.delete(`/investments/${accountId}/holdings/${holdingId}`),
 }
diff --git a/frontend/src/types/index.ts b/frontend/src/types/index.ts
index bda41da..3d6c63e 100644
--- a/frontend/src/types/index.ts
+++ b/frontend/src/types/index.ts
@@ -364,6 +364,21 @@ export interface InvestmentPerformance {
   holdings: InvestmentHolding[]
 }
 
+export interface CreateInvestmentHoldingRequest {
+  symbol: string
+  securityName: string
+  securityType?: string | null
+  shares: number
+  costBasis: number
+  currentPrice?: number | null
+}
+
+export interface UpdateInvestmentHoldingRequest {
+  shares: number
+  costBasis: number
+  currentPrice?: number | null
+}
+
 // Reconciliation
 export interface ReconciliationResponse {
   id: string
diff --git a/frontend/src/views/investments/InvestmentsView.vue b/frontend/src/views/investments/InvestmentsView.vue
index e0bb257..0d60c0d 100644
--- a/frontend/src/views/investments/InvestmentsView.vue
+++ b/frontend/src/views/investments/InvestmentsView.vue
@@ -38,7 +38,8 @@
             <div class="text-caption text-medium-emphasis mb-6">Account Balance</div>
             <v-icon size="48" color="grey-lighten-1" class="mb-4">mdi-chart-pie</v-icon>
             <p class="text-medium-emphasis">No individual holdings tracked for this account.</p>
-            <p class="text-medium-emphasis text-caption">Add holdings to see allocation, cost basis, and performance.</p>
+            <p class="text-medium-emphasis text-caption mb-4">Add holdings to see allocation, cost basis, and performance.</p>
+            <v-btn color="primary" prepend-icon="mdi-plus" @click="openAddDialog">Add Holding</v-btn>
           </v-card>
         </template>
 
@@ -97,7 +98,11 @@
             </v-col>
             <v-col cols="12" md="8">
               <v-card>
-                <v-card-title>Holdings</v-card-title>
+                <v-card-title class="d-flex align-center">
+                  Holdings
+                  <v-spacer />
+                  <v-btn color="primary" size="small" prepend-icon="mdi-plus" @click="openAddDialog">Add Holding</v-btn>
+                </v-card-title>
                 <v-card-text>
                   <v-data-table
                     :headers="holdingsHeaders"
@@ -120,6 +125,16 @@
                         {{ formatPercent(item.gainLossPercent) }}
                       </span>
                     </template>
+                    <template #item.actions="{ item }">
+                      <div class="d-flex align-center ga-1">
+                        <v-btn icon size="x-small" variant="text" @click="openEditDialog(item)">
+                          <v-icon size="small">mdi-pencil</v-icon>
+                        </v-btn>
+                        <v-btn icon size="x-small" variant="text" color="error" @click="confirmDelete(item)">
+                          <v-icon size="small">mdi-delete</v-icon>
+                        </v-btn>
+                      </div>
+                    </template>
                   </v-data-table>
                 </v-card-text>
               </v-card>
@@ -134,7 +149,74 @@
       </v-card>
     </template>
 
-    <v-snackbar v-model="snackbar" color="error" :timeout="3000">{{ snackbarText }}</v-snackbar>
+    <!-- Add/Edit Holding Dialog -->
+    <v-dialog v-model="showHoldingDialog" max-width="500" persistent>
+      <v-card>
+        <v-card-title>{{ editingHolding ? 'Edit Holding' : 'Add Holding' }}</v-card-title>
+        <v-card-text>
+          <v-text-field
+            v-if="!editingHolding"
+            v-model="holdingForm.symbol"
+            label="Symbol"
+            placeholder="e.g. AAPL"
+            :rules="[v => !!v || 'Symbol is required']"
+          />
+          <v-text-field
+            v-if="!editingHolding"
+            v-model="holdingForm.securityName"
+            label="Security Name"
+            placeholder="e.g. Apple Inc."
+            :rules="[v => !!v || 'Name is required']"
+          />
+          <v-text-field
+            v-model.number="holdingForm.shares"
+            label="Shares"
+            type="number"
+            :rules="[v => v > 0 || 'Shares must be greater than 0']"
+          />
+          <v-text-field
+            v-model.number="holdingForm.costBasisPerShare"
+            label="Cost Basis Per Share"
+            type="number"
+            prefix="$"
+            :rules="[v => v >= 0 || 'Cost basis must be non-negative']"
+          />
+          <div v-if="holdingForm.shares > 0 && holdingForm.costBasisPerShare > 0" class="text-caption text-medium-emphasis mb-4">
+            Total Cost Basis: {{ formatCurrency(holdingForm.shares * holdingForm.costBasisPerShare) }}
+          </div>
+          <v-text-field
+            v-model.number="holdingForm.currentPrice"
+            label="Current Price (optional)"
+            type="number"
+            prefix="$"
+            hint="Leave empty to keep existing price"
+            persistent-hint
+          />
+        </v-card-text>
+        <v-card-actions>
+          <v-spacer />
+          <v-btn @click="showHoldingDialog = false">Cancel</v-btn>
+          <v-btn color="primary" :loading="saving" @click="saveHolding">Save</v-btn>
+        </v-card-actions>
+      </v-card>
+    </v-dialog>
+
+    <!-- Delete Confirmation Dialog -->
+    <v-dialog v-model="showDeleteDialog" max-width="400">
+      <v-card>
+        <v-card-title>Delete Holding</v-card-title>
+        <v-card-text>
+          Are you sure you want to delete the holding for "{{ deletingHolding?.symbol }}"? This cannot be undone.
+        </v-card-text>
+        <v-card-actions>
+          <v-spacer />
+          <v-btn @click="showDeleteDialog = false">Cancel</v-btn>
+          <v-btn color="error" :loading="saving" @click="deleteHolding">Delete</v-btn>
+        </v-card-actions>
+      </v-card>
+    </v-dialog>
+
+    <v-snackbar v-model="snackbar" :color="snackbarColor" :timeout="3000">{{ snackbarText }}</v-snackbar>
   </div>
 </template>
 
@@ -144,7 +226,7 @@ import VueApexCharts from 'vue3-apexcharts'
 import { investmentsApi } from '@/services/investments'
 import { useAccountsStore } from '@/stores/accounts'
 import { formatCurrency, formatPercent, accountTypeLabel, accountTypeIcon } from '@/utils/formatters'
-import type { InvestmentPerformance } from '@/types'
+import type { InvestmentPerformance, InvestmentHolding } from '@/types'
 
 const apexchart = VueApexCharts
 
@@ -153,8 +235,23 @@ const accountsStore = useAccountsStore()
 const selectedAccountId = ref<string | null>(null)
 const performance = ref<InvestmentPerformance | null>(null)
 const loading = ref(false)
+const saving = ref(false)
 const snackbar = ref(false)
 const snackbarText = ref('')
+const snackbarColor = ref('success')
+
+// Dialog state
+const showHoldingDialog = ref(false)
+const showDeleteDialog = ref(false)
+const editingHolding = ref<InvestmentHolding | null>(null)
+const deletingHolding = ref<InvestmentHolding | null>(null)
+const holdingForm = ref({
+  symbol: '',
+  securityName: '',
+  shares: 0,
+  costBasisPerShare: 0,
+  currentPrice: null as number | null,
+})
 
 const investmentAccountTypes = ['Retirement401k', 'IRA', 'Brokerage']
 
@@ -202,6 +299,7 @@ const holdingsHeaders = [
   { title: 'Market Value', key: 'marketValue', align: 'end' as const },
   { title: 'Gain/Loss', key: 'gainLoss', align: 'end' as const },
   { title: 'Return', key: 'gainLossPercent', align: 'end' as const },
+  { title: 'Actions', key: 'actions', sortable: false, width: '100px' },
 ]
 
 async function loadPerformance() {
@@ -214,14 +312,89 @@ async function loadPerformance() {
     const { data } = await investmentsApi.getPerformance(selectedAccountId.value)
     performance.value = data
   } catch {
-    snackbarText.value = 'Failed to load investment performance'
-    snackbar.value = true
+    showSnackbar('Failed to load investment performance', 'error')
     performance.value = null
   } finally {
     loading.value = false
   }
 }
 
+function openAddDialog() {
+  editingHolding.value = null
+  holdingForm.value = { symbol: '', securityName: '', shares: 0, costBasisPerShare: 0, currentPrice: null }
+  showHoldingDialog.value = true
+}
+
+function openEditDialog(holding: InvestmentHolding) {
+  editingHolding.value = holding
+  const costBasisPerShare = holding.shares > 0 ? holding.costBasis / holding.shares : 0
+  holdingForm.value = {
+    symbol: holding.symbol,
+    securityName: holding.securityName,
+    shares: holding.shares,
+    costBasisPerShare: Math.round(costBasisPerShare * 100) / 100,
+    currentPrice: holding.currentPrice || null,
+  }
+  showHoldingDialog.value = true
+}
+
+async function saveHolding() {
+  if (!selectedAccountId.value) return
+  saving.value = true
+  try {
+    const totalCostBasis = holdingForm.value.shares * holdingForm.value.costBasisPerShare
+    if (editingHolding.value) {
+      await investmentsApi.updateHolding(selectedAccountId.value, editingHolding.value.id, {
+        shares: holdingForm.value.shares,
+        costBasis: totalCostBasis,
+        currentPrice: holdingForm.value.currentPrice || undefined,
+      })
+      showSnackbar('Holding updated')
+    } else {
+      await investmentsApi.createHolding(selectedAccountId.value, {
+        symbol: holdingForm.value.symbol,
+        securityName: holdingForm.value.securityName,
+        shares: holdingForm.value.shares,
+        costBasis: totalCostBasis,
+        currentPrice: holdingForm.value.currentPrice || undefined,
+      })
+      showSnackbar('Holding added')
+    }
+    showHoldingDialog.value = false
+    await loadPerformance()
+  } catch {
+    showSnackbar('Failed to save holding', 'error')
+  } finally {
+    saving.value = false
+  }
+}
+
+function confirmDelete(holding: InvestmentHolding) {
+  deletingHolding.value = holding
+  showDeleteDialog.value = true
+}
+
+async function deleteHolding() {
+  if (!selectedAccountId.value || !deletingHolding.value) return
+  saving.value = true
+  try {
+    await investmentsApi.deleteHolding(selectedAccountId.value, deletingHolding.value.id)
+    showDeleteDialog.value = false
+    showSnackbar('Holding deleted')
+    await loadPerformance()
+  } catch {
+    showSnackbar('Failed to delete holding', 'error')
+  } finally {
+    saving.value = false
+  }
+}
+
+function showSnackbar(text: string, color = 'success') {
+  snackbarText.value = text
+  snackbarColor.value = color
+  snackbar.value = true
+}
+
 watch(selectedAccountId, () => loadPerformance())
 
 onMounted(async () => {
diff --git a/src/Purrse.Api/Controllers/InvestmentsController.cs b/src/Purrse.Api/Controllers/InvestmentsController.cs
index 5a13771..801fddc 100644
--- a/src/Purrse.Api/Controllers/InvestmentsController.cs
+++ b/src/Purrse.Api/Controllers/InvestmentsController.cs
@@ -2,6 +2,7 @@ using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.EntityFrameworkCore;
 using Purrse.Core.DTOs;
+using Purrse.Core.Models;
 using Purrse.Data;
 using System.Security.Claims;
 
@@ -17,11 +18,14 @@ public class InvestmentsController : ControllerBase
 
     public InvestmentsController(PurrseDbContext db) => _db = db;
 
+    private async Task<Account?> GetAccountIfOwned(Guid accountId) =>
+        await _db.Accounts.FirstOrDefaultAsync(a => a.Id == accountId && a.UserId == UserId);
+
     [HttpGet("{accountId}/holdings")]
     public async Task<ActionResult<List<InvestmentHoldingResponse>>> GetHoldings(Guid accountId)
     {
-        var account = await _db.Accounts.FirstOrDefaultAsync(a => a.Id == accountId && a.UserId == UserId)
-            ?? throw new KeyNotFoundException("Account not found");
+        if (await GetAccountIfOwned(accountId) is null)
+            return NotFound();
 
         var holdings = await _db.InvestmentHoldings
             .Include(h => h.Security).ThenInclude(s => s.Prices)
@@ -55,4 +59,121 @@ public class InvestmentsController : ControllerBase
 
         return Ok(new InvestmentPerformanceResponse(totalMarket, totalCost, totalGL, totalPct, holdings));
     }
+
+    [HttpPost("{accountId}/holdings")]
+    public async Task<ActionResult<InvestmentHoldingResponse>> CreateHolding(Guid accountId, CreateInvestmentHoldingRequest request)
+    {
+        if (await GetAccountIfOwned(accountId) is null)
+            return NotFound();
+
+        var normalizedSymbol = request.Symbol.Trim().ToUpperInvariant();
+
+        var security = await _db.Securities.FirstOrDefaultAsync(s => s.Symbol == normalizedSymbol);
+        if (security is null)
+        {
+            security = new Security
+            {
+                Id = Guid.NewGuid(),
+                Symbol = normalizedSymbol,
+                Name = request.SecurityName.Trim(),
+                SecurityType = request.SecurityType?.Trim()
+            };
+            _db.Securities.Add(security);
+        }
+
+        var holding = new InvestmentHolding
+        {
+            Id = Guid.NewGuid(),
+            AccountId = accountId,
+            SecurityId = security.Id,
+            Shares = request.Shares,
+            CostBasis = request.CostBasis,
+            AsOfDate = DateTime.UtcNow
+        };
+        _db.InvestmentHoldings.Add(holding);
+
+        if (request.CurrentPrice.HasValue)
+            await UpsertSecurityPrice(security.Id, DateTime.UtcNow.Date, request.CurrentPrice.Value);
+
+        await _db.SaveChangesAsync();
+
+        var latestPrice = request.CurrentPrice ?? 0;
+        var marketValue = holding.Shares * latestPrice;
+        var gainLoss = marketValue - holding.CostBasis;
+        var gainLossPct = holding.CostBasis != 0 ? (gainLoss / holding.CostBasis) * 100 : 0;
+
+        return Ok(new InvestmentHoldingResponse(holding.Id, security.Symbol, security.Name,
+            holding.Shares, holding.CostBasis, latestPrice, marketValue, gainLoss, gainLossPct, holding.AsOfDate));
+    }
+
+    [HttpPut("{accountId}/holdings/{holdingId}")]
+    public async Task<ActionResult<InvestmentHoldingResponse>> UpdateHolding(Guid accountId, Guid holdingId, UpdateInvestmentHoldingRequest request)
+    {
+        if (await GetAccountIfOwned(accountId) is null)
+            return NotFound();
+
+        var holding = await _db.InvestmentHoldings
+            .Include(h => h.Security).ThenInclude(s => s.Prices)
+            .FirstOrDefaultAsync(h => h.Id == holdingId && h.AccountId == accountId);
+
+        if (holding is null)
+            return NotFound();
+
+        holding.Shares = request.Shares;
+        holding.CostBasis = request.CostBasis;
+        holding.AsOfDate = DateTime.UtcNow;
+
+        if (request.CurrentPrice.HasValue)
+            await UpsertSecurityPrice(holding.SecurityId, DateTime.UtcNow.Date, request.CurrentPrice.Value);
+
+        await _db.SaveChangesAsync();
+
+        var latestPrice = request.CurrentPrice
+            ?? holding.Security.Prices.OrderByDescending(p => p.Date).FirstOrDefault()?.Price ?? 0;
+        var marketValue = holding.Shares * latestPrice;
+        var gainLoss = marketValue - holding.CostBasis;
+        var gainLossPct = holding.CostBasis != 0 ? (gainLoss / holding.CostBasis) * 100 : 0;
+
+        return Ok(new InvestmentHoldingResponse(holding.Id, holding.Security.Symbol, holding.Security.Name,
+            holding.Shares, holding.CostBasis, latestPrice, marketValue, gainLoss, gainLossPct, holding.AsOfDate));
+    }
+
+    [HttpDelete("{accountId}/holdings/{holdingId}")]
+    public async Task<ActionResult> DeleteHolding(Guid accountId, Guid holdingId)
+    {
+        if (await GetAccountIfOwned(accountId) is null)
+            return NotFound();
+
+        var holding = await _db.InvestmentHoldings
+            .FirstOrDefaultAsync(h => h.Id == holdingId && h.AccountId == accountId);
+
+        if (holding is null)
+            return NotFound();
+
+        _db.InvestmentHoldings.Remove(holding);
+        await _db.SaveChangesAsync();
+
+        return NoContent();
+    }
+
+    private async Task UpsertSecurityPrice(Guid securityId, DateTime date, decimal price)
+    {
+        var existing = await _db.SecurityPrices
+            .FirstOrDefaultAsync(p => p.SecurityId == securityId && p.Date == date);
+
+        if (existing is not null)
+        {
+            existing.Price = price;
+        }
+        else
+        {
+            _db.SecurityPrices.Add(new SecurityPrice
+            {
+                Id = Guid.NewGuid(),
+                SecurityId = securityId,
+                Date = date,
+                Price = price
+            });
+        }
+    }
 }
diff --git a/src/Purrse.Core/DTOs/InvestmentDtos.cs b/src/Purrse.Core/DTOs/InvestmentDtos.cs
index 90676e1..76786e6 100644
--- a/src/Purrse.Core/DTOs/InvestmentDtos.cs
+++ b/src/Purrse.Core/DTOs/InvestmentDtos.cs
@@ -20,3 +20,22 @@ public record InvestmentPerformanceResponse(
     decimal TotalGainLossPercent,
     List<InvestmentHoldingResponse> Holdings
 );
+
+public record CreateInvestmentHoldingRequest(
+    string Symbol,
+    string SecurityName,
+    string? SecurityType,
+    decimal Shares,
+    decimal CostBasis,
+    decimal? CurrentPrice
+);
+
+public record UpdateInvestmentHoldingRequest(
+    decimal Shares,
+    decimal CostBasis,
+    decimal? CurrentPrice
+);
+
+public record UpdateSecurityPriceRequest(
+    decimal Price
+);