Mental health issues are one of the top reasons for global disability. Three of the top 10 reasons for disability in people between the age of 15 and 44 are mental disorders (World Health Report, 2002). Experiencing a lot of stress or anxiety over a long period of time can be the main cause of mental illness. Stress is an inherent part of life that can have major repercussions for social and emotional functioning, leading to the emergence of mental health disorders. Facial expressions are a vital component of emotions, which people can readily notice and react to even without conscious awareness. The human face is said to be a reflection of one's emotions. The human face and facial expressions are the most powerful ways to convey an emotional state. Most of the previous studies of facial expression recognition and emotion detection focused only on seven primary emotions: happiness, sadness, anger, disgust, fear, surprise, and neutral. Stress and anxiety are the two emotional states that have been recently added to the above-mentioned set of emotions and can be measured. These states can be defined as people's reactions when exposed to pressures and demands that do not match their knowledge and abilities, thus putting their management abilities to the test (Franken, R., 1994). This introductory chapter provides an overview of the concept of stress, including its terminologies, classifications, and effects on organisations and individuals. The chapter is structured into nine sections with the objective of developing a conceptual knowledge of stress and its consequences through extensive, sound, and scientific study. The first section deals with the basic concept of stress in general, various definitions of stress, and its various types and stressors, followed by the second section, which deals with the basic concepts of anxiety, types of anxiety, and its signs and symptoms. The third section deals with the physical, mental, and cognitive effects of stress and anxiety on the human body. The fourth section deals with the concept of stress and anxiety's impact on the human face. The sixth section briefly explains the motivation of the study and the need for a stress prediction system. The seventh section presents the various applications of stress prediction system. The eighth section discusses research questions and research objectives, and finally, the ninth section presents the organization of the thesis, followed by a chapter summary.