diff --git a/bgpwtf/invoice/proto/invoice.proto b/bgpwtf/invoice/proto/invoice.proto
index e6caae5..70e6923 100644
--- a/bgpwtf/invoice/proto/invoice.proto
+++ b/bgpwtf/invoice/proto/invoice.proto
@@ -312,9 +312,48 @@
 message SealInvoiceResponse {
 }
 
+message GetInvoicesRequest {
+    // Return all invoices issued in a given year.
+    message ForYear {
+        int32 year = 1;
+    }
+    // Return all invoices issued in a given month of a year.
+    message ForMonth {
+        int32 year = 1;
+        int32 month = 2;
+    }
+
+    oneof range {
+        ForYear for_year = 1;
+        ForMonth for_month = 2;
+    }
+}
+
+message GetInvoicesResponse {
+    // Each chunk may contain an arbitrary amount of invoices, and each
+    // GetInvoices request may return an arbitrary amount of
+    // GetInvoicesResponses in a stream.
+    repeated Invoice invoice = 1;
+}
+
 service Invoicer {
+    // Create an invoice with given data, returning UID. The newly created
+    // invoice is created as a proforma invoice and not yet sealed, ie. not
+    // given a unique, sequential ID.
     rpc CreateInvoice(CreateInvoiceRequest) returns (CreateInvoiceResponse);
+
+    // Get invoice details for a given UID.
     rpc GetInvoice(GetInvoiceRequest) returns (GetInvoiceResponse);
+
+    // Return chunks of a rendered PDF for a given UID. If the invoice is
+    // sealed, the stored PDF will be returned, otherwise a PDF will be
+    // rendered on the fly.
     rpc RenderInvoice(RenderInvoiceRequest) returns (stream RenderInvoiceResponse);
+
+    // Seal invoice, ie. assign it a sequential ID and render it to an
+    // immutable PDF for audit purposes.
     rpc SealInvoice(SealInvoiceRequest) returns (SealInvoiceResponse);
+
+    // Return a summarized detail of invoice data for a given filter.
+    rpc GetInvoices(GetInvoicesRequest) returns (stream GetInvoicesResponse);
 }