A three step photoionizaion process in ytterbium (Yb) atom was investigated experimentally and theoretically. The investigated photoionization scheme consisted of the excitation from ground state ($6s^2,^1S_0$) to the state of $4f^{13}6s^{2}6p$ $(7/2, 3/2)_2$ via firstly excited state (6s6p $^3P_1$) and the ionization by use of the autoionizing state. For the $6s^2\,^1S_0\,-\,6s6p\,^3P_1$ transition, we have measured the resonance line profile and Rabi oscillation. Fitting a set of density matrix equation to the resonance line profile and Rabi oscillation curve, we could measure the amount of phase diffusion of the laser and the oscillator strength of the transition. The effect of the laser spectral characteristics on the selective photoionization was investigated in 6s6p $^3P_1-4f^{13}6s^{2}6p$ $(7/2, 3/2)_2$ transition by using a multi-mode laser (5.2 GHz linewidth) and a single-mode laser (400 MHz linewidth). Notable increase of isotope selectivity was observed only for the case of the single-mode laser and therefore, in this case, we investigated the laser intensity and frequency dependencies of isotope excitation processes. Theoretical interpretation was made by using the rate equations including laser linewidth, Doppler broadening, and natural broadening effects. In the ionization stage, the autoionizing states of ytterbium in $50400 cm^{-1}$ - $60000 cm^{-1}$ energy range were investigated by three-photon polarization spectroscopy. In this work, 17 autoionizing states including many new ones were investigated and some states were suggested for efficient photoionization. For all these states, Fano parameters and J values are measured.
