The book explores the instrumentation and applications of optical tweezers to study statistical physics in soft, bio and nanoscale systems. The first part gives a general introduction about optical tweezers and detailed description of a typical setup along with its calibrations. Then it describes studies of statistical properties in soft matter systems, namely, out-of-equilibrium microrheology in a worm-like micellar system, irreversibility to reversibility crossover in the non-equilibrium trajectories of an optically trapped bead, and tunable Brownian vortices at liquid-air interface. The mechanical manipulation of the nano-systems, i.e. optically driven nano-rotors and the trapping, as well as transportation of palladium decorated single-wall carbon nanotubes using optical tweezers have been discussed in the following chapters. The study of physical property of a bio-inspired system - the cell membrane deformability of human erythrocytes with increasing calcium ion concentration constitutes the last part of the book.