The catalog of 4195 optically confirmed Sunyaev-Zel'dovich (SZ) selected galaxy clusters were detected with signal-to-noise > 4 in 13,211 deg² of sky surveyed by the Atacama Cosmology Telescope (ACT). Cluster candidates were selected by applying a multi-frequency matched filter to 98- and 150-GHz maps constructed from ACT observations obtained from 2008-2018 and confirmed using deep, wide-area optical surveys. The clusters span the redshift range 0.04 < z < 1.91 (median z = 0.52). The catalog contains 222 z > 1 clusters, and a total of 868 systems are new discoveries. Assuming an SZ-signal vs. mass scaling relation calibrated from X-ray observations, the sample has a 90% completeness mass limit of M_500c > 3.8 x 10¹⁴M_sol, evaluated at z=0.5, for clusters detected at signal-to-noise ratio > 5 in maps filtered at an angular scale of 2.40. The survey has a large overlap with deep optical weak-lensing surveys that are being used to calibrate the SZ-signal mass-scaling relation, such as the Dark Energy Survey (4566 deg²), the Hyper Suprime-Cam Subaru Strategic Program (469 deg²), and the Kilo Degree Survey (825 deg²). This HEASARC database table was ingested in February 2021. It contains the ACT DR5 SZ cluster catalog obtained from the LAMDBA website (<a href="https://lambda.gsfc.nasa.gov/product/act/actpol_dr5_szcluster_catalog_info.cfm#catalog">https://lambda.gsfc.nasa.gov/product/act/actpol_dr5_szcluster_catalog_info.cfm#catalog</a>;). This is a service provided by NASA HEASARC .