Military psychology is a specialization within psychology that applies psychological science to promote the readiness of military members, organizations, and operations. Military psychologists provide support to the military in many ways, including through direct clinical care, consultation to military commanders, teaching others and supporting military training; and through research relevant to military operations and personnel.

Military psychology as a field has been growing since the early 20th century, evidence that the demands and needs for psychological clinical and operational application is continuing to grow steadily. There are many stressors associated with military service, including exposure to high-risk training and combat. As such, psychologists are critical support components that assist military leaders in designing appropriate training programs, providing oversight to those programs, and assisting military members as they navigate the challenges of military training and their new lifestyle.

Military psychology covers a wide range of fields throughout the military including operational, tactical, and occupational psychology. Gender differences between military-trained personnel who seek mental health assistance have been extensively studied. Specific examples include post traumatic stress disorder (PTSD) associated with combat, or guilt and family/partner difficulties accompanying extended or frequent deployments due to separation. Clinical providers in military psychology are often focused on the treatment of stress, fatigue, and other personal readiness issues.

Previous wars such as the Korean War, Vietnam War, and World War II provide great insight to the workings and practices of military psychology and how the practices have changed and assisted the military over the years.

The military is a group of individuals who are trained and equipped to perform national security tasks in unique and often chaotic and trauma-filled situations. These situations can include the front-lines of battle, national emergencies, counter-terrorism support, allied assistance, or the disaster response scenarios where they are providing relief-aid for the host populations of both friendly and enemy states. Though many psychologists may have a general understanding with regards to a humans response to traumatic situations, military psychologists are uniquely trained and experienced specialists in applied science and practice among this special population. While the service members may be providing direct aid to the victims of events, military psychologists are providing specialized aid to both members, their families, and the victims of military operations as they cope with the often "normal" response or reaction to uncommon and abnormal circumstances. Military psychologists can assess, diagnose, treat and recommend the duty status most suitable for the optimal well-being of the individual, group, and organization. Through the use of group therapy, individual therapy, and behavior modification, these psychologists actively treat psychological disorders, most commonly emotional trauma. When counseling members of a military personnel's family, they are most often tasked with providing grief counseling after the loss of a loved one in the line of duty. Events that affect the mental state, resilience or psychological assets and vulnerabilities of the warrior and the command are where military psychologists are most equipped to meet the unique challenges and provide expert care and consultation to preserve the behavioral health of the fighting force.

In addition to the specialized roles previously mentioned, military psychologists often provide support to many non-healthcare-related activities. For example, military psychologists may provide their expertise and training in the consultation to hostage negotiations. Military psychologists are not hostage negotiators; however, they often consult [ation] with those directly communicating with hostage-takers in a manner that seeks the safety and protections of all involved. Military psychologists may also apply their science to aviation selection and training, to the study and application of survival training, and the selection of personnel for special military duties.

Another common practice domain for military psychologists is in performing fitness for duty evaluations, especially in high risk and high reliability occupations. The types of fitness evaluations include both basic entry examinations and career progression examinations such as those conducted when individuals are seeking promotion, higher-classification clearance status, and specialized, hazardous, and mission critical working conditions. When operational commanders become concerned about the impact of continuous, critical, and traumatic operations on those in their command, they often consult with a military psychologist.

The fitness evaluations might lead to command directed administrative actions or provide the information necessary to make decisions by a medical board or other tribunal and must be thoroughly conducted by non-biased individuals with the experience and training necessary to render a professional opinion that is critical to key decision makers. Military psychologists must be well versed in the art and science of psychology as specialized applied practice professionals. They must also be highly competent generalists in the military profession, and be able to understand both professions well enough to examine human behavior in the context of military operations. It takes the psychologist several years beyond the doctorate to develop the expertise necessary to understand how to integrate psychology with the complex needs of the military.