Professor Roger Y. Tsien is a renowned world leader in chemical biology and biochemistry whose pioneering work in fluorescence sensing and imaging has revolutionized virtually all of experimental biology. He is an insightful scientist, and a cordial colleague and mentor; always invigorating with his ideas and energy, and inspiring with his vision. There are 18 contributions in this special section, covering the topics of developing infrared fluorescence microscopy, fluorescent dyes, and probes. The application of these tools and probes also indicates their broad impact, with the model systems of their applications ranging from tumors and cancers to cardiomyocytes and cardiovascular systems. To date, Prof. Tsien continues to lead and contribute to the emerging fields of molecular and cellular imaging as well as biomedical optics.