With the advent of ultra high-throughput genomic and epigenetic assays, generation of molecular data has skyrocketed. With the change in data type and volume, we are experiencing an acute need for more sophisticated techniques to model and infer pathways. Pathway informatics is one of the frontiers in the field of biological data analysis. It involves curation of unstructured information from publicly available literature, database building, statistical analysis of gene sets, mathematical modeling of pathways, and visualization. In this article we review various components of pathway informatics including the types of pathways, their corresponding databases, and other types of resources, as well as various computational and mathematical approaches for information fusion and inferences.