Alternative splicing (AS) is a widespread process facilitating the generation of regulatory and proteomic complexity. However, the function of the vast majority of AS events detected to date is unknown, and landscapes of regulated AS remain to be identified. To contribute to address these challenges, we present VAST-DB, a massive resource of genome-wide quantitative profiles generated using vast-tools (https://github.com/vastgroup/vast-tools) for all main classes of AS events of a wide range of human, mouse and chicken tissues, cell types and developmental stages. The resulting atlas of AS events reveals extensive new intergenic and intragenic regulatory and functional relationships involving different classes of AS events, as well as previously unknown conserved landscapes of tissue-regulated exons. We also report and validate hundreds of AS events that are alternatively spliced in virtually all profiled tissue and cell types. These AS events are highly enriched in genes that encode transcription factors and DNA binding proteins, and single cell RNA-seq data show that they are usually predicted to generate protein isoforms that co-exist in the same cell. Finally, we also provide mapping of these AS events to protein regions and experimentally determined or modeled protein structures. Our AS atlas thus provides a valuable basis for new explorations of splice isoform regulation and function in an evolutionary context.