As compared to wired systems, wireless communication systems operate in a distinct environment - understanding the wireless propagation characteristics is crucial to understand the design and analysis of wireless networks. Specifically, the wireless medium introduces several challenges: the signal strength attenuates substantially with distance, unpredictable fluctuations in received signal strength, called fading, occur due to multipath propagation or atmospheric effects, and obstacles like walls, glass, and foliage can hinder signal transmission. Additionally, these impacts are frequency dependent. This chapter examines various models used to analyse these challenges in wireless communication systems, including distance-based pathloss models for predicting signal attenuation, material penetration loss for understanding how different materials affect signal propagation, and fading models at both small and large scales. Additionally, strategies to overcome fading effects including adding a fading margin and key channel parameters like delay spread, coherence time, and coherence bandwidth are discussed.