Background: Millions of older Americans have to practice social distancing due to the COVID-19 pandemic. It is anticipated that this will need to continue for many older people until an effective vaccine is available. Due to these restrictions, most older people cannot take part in their regular physical and social activities. Physical deconditioning occurs rapidly when older people reduce their activity level. This increases the risk of people becoming so weak that it limits their ability to do basic mobility activities like climbing stairs and walking outdoors. Muscle weakness and balance impairments are also major risk factors for falls and fall-related injuries, including fractures. Because people have lost their usual sources of social connection, there is likely to be an increased incidence of loneliness (i.e. the feeling of being isolated), social isolation (i.e. the lack of social connection and support) and depression among older people. Loneliness and social isolation were already serious problems for older people before this pandemic. Many organizations have put in place telephone calls by volunteers or paid employees to reduce loneliness and social isolation by engaging in friendly companionship conversations. However, there is evidence that tele-interventions by lay people that use brief behavioral activation coaching are significantly more effective in changing important health outcomes than conversational calls. Methods: This study will explore the feasibility, acceptability and preliminary evidence of efficacy of telephone-based Behavioral Activation Coaching telephone calls to reduce loneliness and prevent deconditioning in n=50 older people recruited from primary care practices in Boston or senior living/assistive living centers near Baltimore. The intervention will be delivered entirely remotely in 10 sessions over 4 months. Outcomes include measures of feasibility, safety and acceptability. Efficacy will be explored by measuring changes in daily steps walked using a wearable sensor, loneliness, function, disability, social isolation, depression, anxiety, and health care utilization. Patient reported outcomes will be measured by trained telephone assessors at baseline - and 4-months post enrollment. Implications: If the Behavioral Activation Coaching telephone calls are found to be effective this model could be quickly disseminated to volunteer organizations, health systems or businesses that wish to support people who are social isolating due to COVID-19. The materials and resources to implement the Behavioral Activation Coaching will be made freely available online.