An improved piercing fitment assembly for mounting to a flexible container is provided, whereby the contents of the container are dispensed by piercing a pierceable portion of a cap using a fluid transfer device. The piercing fitment assembly is easy to use as a relatively minimal amount of force is required for piercing and establishing fluid transfer. It also has a locking system which locks the fluid transfer device into a dispensing state and also forms a reliable seal between the cap and the fluid transfer device which minimizes the risk of unwanted spillage. The fitment assembly comprises: a spout connected in fluid communication to the container; a cap having a pierceable portion sealing an end of the spout and a fluid transfer device having a leading tooth to initiate piercing of the pierceable portion of the cap.