Nanotechnology is the key to a new, noninvasive photoacoustic imaging technique that could detect early stages of disease tissues. The combination of photoacoustic imaging with nanotechnology holds promise for determining the structural and functional properties of tissues with enhanced sensitivity and specificity and for monitoring the treatment of diseases. In this chapter, we described in detail photoacoustic reconstruction methods and imaging systems. We also review the recent advances in nanoparticles and their in vivo applications in the field of photoacoustic imaging.