We are pleased to offer readers of the Journal of Mathematical Chemistry this Special Issue consisting of papers on the topics discussed at the 13th International Conference of Computational and Mathematical Methods in Science and Engineering, CMMSE—2013, held at Almeria, Spain, June 24–28, 2013. This special issue includes not only papers actually presented at the Conference, but also some additional, specially selected papers, which are thematically related to the subjects discussed at the conference, and provide additional overview and a fuller coverage of the field typically covered by the CMMSE meetings.Since its foundation in Milwaukee in 2000, the CMMSE organization has provided a stimulating annual forum for researchers involved in some of the interdisciplinary areas of applied mathematics and natural sciences, especially, chemistry. Most of these researchers and contributors have found in CMMSE a fruitful arena in which to disseminate their results and advances to the research ...