Surgical instruments and end effectors therefor are disclosed. In various implementations, the surgical instrument includes an elongated shaft assembly that defines a longitudinal tool axis. An elongated channel of an end effector is movably coupled to the elongated shaft assembly for selective pivotal travel about a pivot axis that is transverse to the longitudinal tool axis upon application of articulation motions thereto. The elongated channel may be configured to operably support a surgical staple cartridge. An anvil assembly is pivotally coupled to the elongated channel for selective pivotal travel relative thereto between open and closed positions about the pivot axis upon application of closing and opening motions thereto. In some implementations, the anvil assembly comprises a two part assembly.