Use of antiretroviral therapy (ART) increasing in Sub Saharan Africa has offered hope to HIV-infected patients. HIV treatment success depends on continuous high levels of adherence (> 90-95%), proven a major problem among many ART users. To support adherence, it’s important to understand causes of non-adherence & use reliable tool to measure adherence, both aspects are limited in low resource countries. This book identifies reliable and valid tools to measure adherence and contributes to improved understanding of challenges patients face when taking ART. Studies were conducted to examine feasibility and validity of adherence measurement tools in rural Tanzania and findings are reported in chapter 2, 3 & 4. Feasibility of use of Medication Event Monitoring System-caps (MEMS) to measure adherence was conducted (chapter 2), upon success of this study, MEMS were used to study adherence to TB-medication (chapter 3). The second line of research deals with understanding determinants of adherence, findings suggest the need to replace maladaptive coping skills like denial and alcohol use with adaptive coping skills, these findings and others are reported in chapter 5 &6 of this book.