In the SWOPT project we are developing an optoacoustic system that can display individual, living cells and their function deep in the tissue. We achieve this by using markers that bind to cells that we want to see or are produced by them and whose signal we can switch on and off in the image using a light pulse. This allows us to hide the disturbing background as desired. SWOPT is a novel imaging technology that will break through the penetration limits of optical microscopy to visualize individual cells and their function in vivo through several millimeters to centimeters of depth. SWOPT will exploit (1) optoacoustic imaging, a modality which combines signal generation similar to optical imaging with the whole animal imaging capability of ultrasound readout, and uniquely augment it with (2) photoswitching to resolve signals from single labeled cells from deep within live tissue. This will achieve volume sampling abilities surpassing any optical microscopy by at least three orders of magnitude (> 5 x 5 x 5 mm imaging volume). SWOPT will develop the necessary breakthrough instrumentation and concepts: unique multiplexed diode illumination, novel ultra-wideband transducer technology, dedicated inversion algorithms that incorporate photoswitching in the three-dimensional reconstructions, and uniquely tailored classes of photo-switching transgene and synthetic molecular tools. The exceptional capabilities of SWOPT will be demonstrated by proof-of-concept work resolving cellular dynamics and functions in a whole tumor in a model of renal cancer in vivo.