A method and assembly are disclosed for interfacing between a drug cartridge and a drug delivery device. Optionally, the drug delivery device includes a compartment that retains the cartridge during drug delivery and/or a stopper pushing assembly mounted to the device behind (proximal to) the compartment. In some embodiments, the cartridge may be inserted laterally into the compartment in front of the pushing assembly. For example, the delivery device may include a moving cartridge bay. The cartridge is optionally inserted into the bay and/or the bay and cartridge optionally move into the cartridge compartment. Alternatively or additionally, the cartridge compartment may have a proximal opening into which the cartridge is inserted and/or the pushing assembly may be moved into position after insertion of the cartridge. In some embodiments the cartridge may have a distal seal that is broken by a longitudinal movement.
