This chapter provides an overview of research on the variables that influence attitude change, focusing on the processes by which these variables affect persuasion. It begins by discussing the importance of attitudes in contemporary social psychology and the complexity of the O.J. Simpson trial as a case study. The chapter then reviews the historical foundations of attitude change research, highlighting the contributions of Carl Hovland and Leon Festinger. It introduces the Elaboration Likelihood Model (ELM) and explains how it differentiates between high and low-effort processes in attitude change. The ELM posits that people can process information through central or peripheral routes, with high elaboration leading to reasoned attitudes and low elaboration leading to weaker attitudes. The chapter also discusses the multiple roles of variables in influencing attitudes, meaning that the same variable can affect attitudes through different processes at different points along the elaboration continuum. Finally, it explores the determinants and dimensions of elaboration, including personal relevance, message repetition, and individual differences in motivation and ability to process information. The chapter concludes by discussing relatively objective and biased information processing, default biases, and the potential for bias correction.This chapter provides an overview of research on the variables that influence attitude change, focusing on the processes by which these variables affect persuasion. It begins by discussing the importance of attitudes in contemporary social psychology and the complexity of the O.J. Simpson trial as a case study. The chapter then reviews the historical foundations of attitude change research, highlighting the contributions of Carl Hovland and Leon Festinger. It introduces the Elaboration Likelihood Model (ELM) and explains how it differentiates between high and low-effort processes in attitude change. The ELM posits that people can process information through central or peripheral routes, with high elaboration leading to reasoned attitudes and low elaboration leading to weaker attitudes. The chapter also discusses the multiple roles of variables in influencing attitudes, meaning that the same variable can affect attitudes through different processes at different points along the elaboration continuum. Finally, it explores the determinants and dimensions of elaboration, including personal relevance, message repetition, and individual differences in motivation and ability to process information. The chapter concludes by discussing relatively objective and biased information processing, default biases, and the potential for bias correction.