The concept of similarity is traceable in various areas of computer science and other disciplines. One of the most visible applications of this concept is similarity data retrieval. This search paradigm has become important especially due to the current phenomenon of data explosion that can be noticed in two dimensions: volumes of data produced today are rapidly increasing, and the diversity of data types is growing. The talk addresses the problem of an efficient management of very large datasets on the basis of similarity. We model data and similarity using the metric space, which is a very universal and extensible concept. One of the main results of our long-term work in this area is a very universal large-scale distributed system for similarity indexing and searching. We have a fully functional prototype implementation of this system - several demonstrations will be part of the talk. The rough outline of the talk is the following: - motivation of the research, current state of the art, - fundamental principles of the similarity search based on metric space model, - peer-to-peer networks and their utilization for distributed data structures design, - description of our specific approach - M-Chord, M-Tree, system architecture, - content-based search on digital images - MPEG-7 descriptors and their combinations, - demonstration of a prototype system for similarity search in a collection of 50 million digital images downloaded from Flickr (photos sharing system), - face-recognition demo.