Two-photon absorption is a photophysical process with diverse applications in medicine (photodynamic therapy), neurophysiology, cell biology (microscopy, photo-activated drugs) and biomedical engineering (fabrication of micro-needle arrays and tissue scaffolds). Many of these applications will only have a major impact when better dyes become available with stronger two-photon absorption, as well as improved secondary properties (photostability, biocompatibility, etc). Advances in optical engineering will also be critical. Two-photon absorption is an important newly emerging supra-discipline at the intersection of Biology, Chemistry, Physics and Engineering. This network will be the first initiative of its kind in this area. TOPBIO will train young researchers in many different aspects of the field, by coupling together research groups with internationally recognized expertise in synthesis, molecular design, theory, photophysics, photobiology, cell biology, engineering, nanotechnology, microscopy and laser physics. We aim not only to train ESR and ER in an interdisciplinary manner but also (by developing new generations of functional dyes and applying them in real biomedical applications) to improve the quality of life in Europe and to strengthen the EU economy. TOPBIO will provide an excellent mechanism for promoting interdisciplinary training, by exchanging PhD students on secondments between collaborating laboratories, through regular progress meetings, workshops and tutorial schools. TOPBIO brings together leading experts from universities and private sector organizations across Europe. It has an exceptional ratio of private to academic partners (1:2). The perfect match of complementary expertise, multidisciplinarity, high involvement of companies and focus on the real needs of society will enable us to deliver high quality training in skills which are perfectly matched to the needs of future employers, thus producing a workforce which will be in high demand.