We present the first Catalog of Low Ionization Emission Line Galaxies (LINERs or Liners, which is the simplest name, and which we shall adopt in what follows). The Catalog "MCL" (Multifrequency Catalog of Liners), contains 476 entries and contains both broad-band and monochromatic emission data (ranging from radio to X-ray frequencies) of colors, and other data compiled from the literature and various data bases, as indicated in the references. Most of the galaxies can be considered "pure" Liners on the basis of the Veilleux & Osterbrock (1987ApJS...63..295V) classification as suggested by Ho, Filippenko, & Sargent (1997ApJS..112..315H). However, a considerable number of transition (Liners-H II or Liners-Starburst) objects are also included. One of the open questions, is whether Liners should be considered as a class of galaxies (like Seyfert galaxies for instance) or rather, as an heterogeneous group of objects. We believe the study of Liners as a group is very interesting, precisely because they very likely represent a transition between non-thermal and starburst activity, and probably also between "active" and "non- active" galaxies. This catalog may be used as a basis for statistical research. A preliminary discussion of the main statistical properties of Liners, in the range from radio to X-ray frequencies, is given here.