ExpressionSieve? combines the best practice of statistical analysis, software engineering, bioinformatics and complex data visualization. ExpressionSieve? is aimed at providing not only set of basic tools for expression analysis, but also tools bridging between expression data and other domain data, such as gene ontology, pathway, genomics, literature, biochemical assay, clinical data, mass spectrometry data, etc. ExpressionSieve? is a versatile tool for disease research, drug discovery, and system biology.