Handed a spectrum, the work begins. In this chapter, we explain how one takes a spectrum and objectively locates and quantifies the statistically significant absorption features peppered throughout. We describe a continuum normalization method that is objective and provides an error model. Multiple spectra may be co-added to improve signal to noise. For objectively locating absorption features, we present a scanning algorithm weighted by the line spread function and optimized for weak lines. Multiple absorption lines arising in rich absorption systems can be found using autocorrelation methods, and one such method is described. To analyze absorption systems, a systemic absorber redshift is determined, and the wavelength scale of all absorption profiles is converted to and aligned in the absorber’s rest-frame velocity. For high-resolution profiles, methods are presented for measuring equivalent widths and quantifying kinematics directly from pixel flux decrements. These include velocity spreads containing 90% of total optical depth and other flux decrement weighted velocity moments. We conclude with detailed methods for building composite two-point velocity correlation functions.