Denial has been an integral part of the psychological and disability literature for more than 100 years. Yet, denial is an elusive concept and has been associated with mixed, indeed conflicting, theoretical perspectives, clinical strategies, and empirical findings. In this two-part article, the author provides an overview of the existing literature on denial that addresses the most prominent and rehabilitation-relevant features of it. Part I provides a generic yet clinically based discussion of denial and focuses on the following: historical perspective of denial, the definitions of denial, the types or forms of denial most often encountered in the literature, the functions served by denial, the indicators or markers most frequently associated with denial, the dynamics and processes inherent in the operation of denial, and the costs and benefits of denial.