The Accelerator Neutrino Neutron Interaction Experiment (ANNIE) is a 26-tonne water Cherenkov detector located in the Booster Neutrino Beam at Fermilab. The water is loaded with gadolinium, greatly improving neutron detection efficiency. This enables ANNIE to make measurements of neutron multiplicity for beam-induced neutrino interactions. In addition, ANNIE serves as a testbed for new technologies, including Water-based Liquid Scintillator (WbLS) and Large Area Picosecond Photodetectors (LAPPD). This talk will provide an overview of the ANNIE physics and R&D programme.