Due to decreasing resources, living in urban regions focus on sustainability in many aspects, including transportation. Sustainable transportation encourages non-motorized modes of walking and cycling as well as public transit (which also relies on walking while accessing a station), as well. However, walking as a mode is still a big mystery itself that needs further attention and research effort especially in the evaluation part. So far, the planners have discussed the concepts of walking and walkability, while engineers have mostly focused on Pedestrian Level of Service (PLOS). The scope of the problem is reflected in the diversity, and consequent inconsistency, in the available PLOS methods, which is one of the problems addressed in this chapter. The second and the bigger problem is the gap between the planning and engineering approaches in evaluating PLOS and walkability producing no consensus or clear relationship between the two, even though they overlap greatly.