  The gamma-ray sky from several hundred keV to $\sim$ a hundred MeV has
remained largely unexplored due to the challenging nature of detecting gamma
rays in this regime. At lower energies, Compton scattering is the dominant
interaction process whereas at higher energies pair production dominates, with
a crossover at about 10 MeV depending on the material. Thus, an instrument
designed to work in this energy range must be optimized for both Compton and
pair-production events. The All-sky Medium Energy Gamma-ray Observatory (AMEGO)
is a NASA Probe-class mission concept being submitted to the Astro2020 review.
The instrument is designed to operate from 200 keV to $>$10 GeV and is made of
four major subsystems: a plastic anti-coincidence detector for rejecting
cosmic-ray events, a silicon tracker for tracking pair-production products and
tracking and measuring the energies of Compton-scattered electrons, a CZT
calorimeter for measuring the energy and location of Compton scattered photons,
and a CsI calorimeter for measuring the energy of the pair-production products
at high energies. A prototype instrument comprising each subsystem is currently
being developed in preparation for a beam test and a balloon flight. In this
contribution we discuss the current status of the prototype subsystems.
