This article discusses propagation measurements and models for wireless communications channels, focusing on how signals propagate through various environments such as outdoor, indoor, and between floors. It explains the three main propagation mechanisms: reflection, diffraction, and scattering, and their effects on signal transmission. The article also covers key propagation parameters like path loss and multipath delay spread, and how they influence communication systems. It describes different types of wireless environments, including macrocells and microcells, and discusses the challenges of predicting signal behavior in these environments. The article also addresses the importance of accurate propagation models for designing reliable wireless communication systems, and highlights the role of statistical and deterministic models in predicting signal behavior. It discusses the impact of building structures on signal propagation, and the use of computer-aided design tools for predicting indoor propagation. The article concludes by emphasizing the need for new and novel ways of classifying wireless environments to achieve ubiquitous personal communications.This article discusses propagation measurements and models for wireless communications channels, focusing on how signals propagate through various environments such as outdoor, indoor, and between floors. It explains the three main propagation mechanisms: reflection, diffraction, and scattering, and their effects on signal transmission. The article also covers key propagation parameters like path loss and multipath delay spread, and how they influence communication systems. It describes different types of wireless environments, including macrocells and microcells, and discusses the challenges of predicting signal behavior in these environments. The article also addresses the importance of accurate propagation models for designing reliable wireless communication systems, and highlights the role of statistical and deterministic models in predicting signal behavior. It discusses the impact of building structures on signal propagation, and the use of computer-aided design tools for predicting indoor propagation. The article concludes by emphasizing the need for new and novel ways of classifying wireless environments to achieve ubiquitous personal communications.