Some highlights of the book are as follows. It is the first book that summarizes and describes in detail the principles and applications of endoscopic imaging. Four sections in the book illustrate the essential principles of endoscope and light–tissue interactions, which demonstrate the underlining optical processes and equations. Figure 1.3 (p. 9) clearly illustrates the energy levels of molecules with major processes including absorption, fluorescence, Raman, two-photon fluorescence, and second harmonic generation (SHG). Various important elements of the endoscope are reviewed. Several key coefficients in tissue are also clearly presented, including the absorption, scattering, and attenuation coefficients, , , , with , and the reduced scattering coefficient in tissue (Table 3.1, p. 34). Values of and are given in Fig. 3.3 (p. 35) for lung tissue. The inverses of these coefficients lead to the penetration lengths in tissue, where is the absorption length, is the mean free scattering length, and is the transport length, i.e., the travel distance to change the photon direction by 90 deg. Also, , where is the anisotropic angular deflection, , and is the scattering angle. Typical values for is and is 330 μm for the lung. The transmission () of the unscattered light, also known as the ballistic light, is described by Beer’s law, , where is the penetration distance into the tissue (Eq. 3.12, p. 33). The ballistic and snake photons are known to carry image information in tissues for OCT, one-photon and two-photon microscopy, spectroscopy, etc.