The Planck Sunyaev-Zeldovich Cluster catalogs contain a list of galaxy clusters detected through the Sunyaev-Zel'dovich effect (SZ) and consist of candidate sources that were detected using multifrequency algorithms that use the distinct spectral signature of such clusters. This version of the SZ catalogs, a component of Planck Data Release 1, is derived from the data acquired by Planck between August 13 2009 and November 26 2010.Three pipelines are used to detect SZ clusters: two independent implementations of the Matched Multi-Filter (MMF1 and MMF3), and PowellSnakes (PwS). The main catalog is constructed as the union of the catalogs from the three detection methods. The individual catalogs are provided for the expert user in order to assess the consistency of the pipelines. The union catalogue contains the coordinates and the signal-to-noise ratio of the detections and a summary of the external validation information, including external identification of a cluster and its redshift if it is available.