UNEP’s International Methane Emissions Observatory (IMEO) launched the Methane Alert and Response System (MARS) in a pilot phase at COP-27 and a fully-operational phase at COP-28. MARS increases transparency and accelerates implementation of the Global Methane Pledge (GMP) by bringing together four critical components: (1) satellite detection of large sources of anthropogenic methane emissions, (2) notification of relevant stakeholders about these detected emissions, (3) assessment and mitigation of emission events and (4) tracking and documentation of events, including public sharing of data. This document provides an overview of the scientific principles and methodologies employed by UNEP IMEO and its partner organizations to detect and quantify methane point source emissions from satellites. While this document is not comprehensive in its descriptions, additional information can be found in the published scientific literature citations found throughout this document. UNEP IMEO satellite methane data is published via the UNEP IMEO Methane Data portal.