  The All-sky Medium Energy Gamma-ray Observatory (AMEGO) is a Probe-class
mission concept that will provide essential contributions to multimessenger
astrophysics in the next decade. AMEGO operates both as a Compton and pair
telescope to achieve unprecedented sensitivity between 200 keV and $>$5 GeV.
The instrument consists of four subsystems. A double-sided strip silicon
Tracker gives a precise measure of the first Compton scatter interaction and
tracks of pair-conversion products. A novel CdZnTe Low Energy Calorimeter with
excellent position and energy resolution surrounds the bottom and sides of the
Tracker to detect the Compton-scattered photons which enhances the polarization
and narrow-line sensitivity. A thick CsI High Energy Calorimeter contains the
high-energy Compton and pair events. The instrument is surrounded by a plastic
anti-coincidence detector to veto the cosmic-ray background. We have performed
detailed simulations to predict the telescope performance and are currently
building a prototype instrument. The AMEGO prototype, known as ComPair, will be
tested at the High Intensity Gamma-Ray Source in 2021, followed by a balloon
flight in Fall of 2022. In this presentation we will give an overview of the
science motivation, a description of the observatory, and an update of the
prototype instrument development.
