diff --git a/bgpwtf/invoice/main.go b/bgpwtf/invoice/main.go
index 5133010a..ae17dbb6 100644
--- a/bgpwtf/invoice/main.go
+++ b/bgpwtf/invoice/main.go
@@ -130,6 +130,10 @@ func (s *service) SealInvoice(ctx context.Context, req *pb.SealInvoiceRequest) (
 	return &pb.SealInvoiceResponse{}, nil
 }
 
+func (s *service) GetInvoices(req *pb.GetInvoicesRequest, srv pb.Invoicer_GetInvoicesServer) error {
+	return status.Error(codes.Unimplemented, "unimplemented")
+}
+
 func init() {
 	flag.Set("logtostderr", "true")
 }
diff --git a/bgpwtf/invoice/proto/invoice.proto b/bgpwtf/invoice/proto/invoice.proto
index e6caae58..70e69232 100644
--- a/bgpwtf/invoice/proto/invoice.proto
+++ b/bgpwtf/invoice/proto/invoice.proto
@@ -312,9 +312,48 @@ message SealInvoiceRequest {
 message SealInvoiceResponse {
 }
 
-service Invoicer {
-    rpc CreateInvoice(CreateInvoiceRequest) returns (CreateInvoiceResponse);
-    rpc GetInvoice(GetInvoiceRequest) returns (GetInvoiceResponse);
-    rpc RenderInvoice(RenderInvoiceRequest) returns (stream RenderInvoiceResponse);
-    rpc SealInvoice(SealInvoiceRequest) returns (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);
 }