Femtosecond fiber lasers are becoming an enabling technology for biomedical imaging and diagnostics from the bench to the bedside. Techniques used for achieving mode locked fiber lasers are discussed. These techniques include polarization shaping, pulse shaping, and spectral shaping. Mode locked fiber lasers operating at 1 μm, 1.55 μm, 2 μm and their harmonic generations (780-800 nm, 515-532 nm, 344-355 nm, 257-266 nm) are discussed. By using dispersion managed amplifiers, amplification and compression of 100 fs femtosecond pulses to 10 watts were demonstrated. These femtosecond fiber lasers are packaged in compact and robust modules and passed long term operation test without any degradation, and proved to be reliable light sources for clinic applications.