DETCHEM stands for DETailed CHEMistry. A package of software tools specifically designed for the modeling and simulation of reacting flows, in particular to heterogeneous systems such as catalysis, materials synthesis, fuel cells. Modeling complex chemical reactions and reactors had always been a challenge, and the ever increasing demand to model reactors calls in for efficient computational tools and algorithms. DETCHEM is a collection of software tools: an outcome of intense academic research; tailored to meet the needs of academia and industry where the challenge is the precise modeling of reactors and processes with complex chemistry models. The core of DETCHEM is a collection of routines for the calculation of chemical reaction rates, species transport, and thermodynamic properties called the library modules. The reactors models are built on top of this library in a modular way covering wide range of applications. Nowadays DETCHEM is widely used in academic as well as in industrial research (chemical, automotive, petrochemical, energy etc.). The potential of DETCHEM lies in the use of elementary step reaction mechanisms in modeling surface and/or gas-phase chemistry. In many applications, the huge number of chemical species and reactions makes the complete system simulation a prohibitive task for commercial CFD codes which are mostly written for general purpose applications. DETCHEM uses state of the art numerical algorithms for the solution of huge equations systems arising from the physico-chemical models for the simulation of special applications, and thus saving the computational time that otherwise could have been prohibitive with multi-purpose CFD software.