diff --git a/src/Qbil/Models/InvoiceInterface.php b/src/Qbil/Models/InvoiceInterface.php
index b7c4460..352cb62 100644
--- a/src/Qbil/Models/InvoiceInterface.php
+++ b/src/Qbil/Models/InvoiceInterface.php
@@ -6,5 +6,21 @@
 
 interface InvoiceInterface
 {
-
+    /**
+     * @return InvoiceLineInterface[]
+     */
+    public function addInvoiceLine();
+    public function getRelation();
+    public function getSubsidiary();
+    public function getSupplierInvoiceNumber();
+    public function getAmount();
+    public function getVatAmount();
+    public function getInvoiceDate();
+    public function getDueDate();
+    public function getCurrency();
+    public function getTheirVatRegistration();
+    public function getOurVatRegistration();
+    public function getInvoiceLines();
+    public function getOrder();
+    public function getContract();
 }
\ No newline at end of file
diff --git a/src/Qbil/Models/InvoiceLine.php b/src/Qbil/Models/InvoiceLine.php
index 69d7297..c13831e 100644
--- a/src/Qbil/Models/InvoiceLine.php
+++ b/src/Qbil/Models/InvoiceLine.php
@@ -77,22 +77,6 @@ public function getAllocatedInvoice()
         return $this->allocatedInvoice;
     }
 
-    /**
-     * @param mixed $type
-     */
-    public function setType($type)
-    {
-        $this->type = $type;
-    }
-
-    /**
-     * @param $allocatedInvoice
-     */
-    public function setAllocatedInvoice($allocatedInvoice)
-    {
-        $this->allocatedInvoice = $allocatedInvoice;
-    }
-
     /**
      * @return mixed
      */
diff --git a/src/Qbil/Models/InvoiceLineInterface.php b/src/Qbil/Models/InvoiceLineInterface.php
index d1e66a5..b70009a 100644
--- a/src/Qbil/Models/InvoiceLineInterface.php
+++ b/src/Qbil/Models/InvoiceLineInterface.php
@@ -6,5 +6,11 @@
 
 interface InvoiceLineInterface
 {
-
+    public function getOrder();
+    public function getQuantity();
+    public function getAmount();
+    public function getPrice();
+    public function getType();
+    public function getAllocatedInvoice();
+    public function getPurchaseContract();
 }
\ No newline at end of file