This report presents implementation and early impact results from a random assignment evaluation of the Young Adult Internship Program (YAIP), a subsidized employment program for young people in New York City who have become disconnected from school and work. Operated by various provider agencies, YAIP offers disconnected youth between the ages of 16 and 24 a temporary paid internship, as well as various support services. The YAIP evaluation is part of the larger Subsidized and Transitional Employment Demonstration. From July 2013 to March 2014, researchers assigned nearly 2,700 young people at random to either a program group, which was offered YAIP services, or to a control group, which was not offered those services. The YAIP evaluation will measure outcomes for both groups over time to assess whether YAIP services led to better outcomes for the program group compared with those of the control group. This report is the first of two focused on the YAIP evaluation. It provides a detailed description of the YAIP model, assesses its implementation, and examines whether the program improved young people's outcomes during the first year after study enrollment. Overall, the implementation study concluded that the YAIP program was well implemented across provider agencies and that participation rates were high. An analysis of youth outcomes indicates that program group members were more likely than control group members to receive employment and other types of support. In part due to the offer of a paid internship, the program group was also more likely to work and had higher earnings in the year following random assignment. Additional follow-up will be necessary to assess YAIP's longer-term effects on employment and earnings, as well as other key outcomes. The following are appended: (1) Survey Response Bias Analysis; (2) YAIP Employer/Supervisor and Participant Program Experiences; (3) Four-Month Impacts on Employment, Psychosocial Outcomes, and Personal Well-Being; (4) One-Year Impacts on Key Outcomes by Subgroup; (5) Variation in Key Baseline Characteristics, Participation Outcomes, and Participant Program Experiences, by YAIP Location; and (6) Control Group Members' Future Expectations and Perspectives on Obstacles Preventing Goal Achievement. [MDRC and subcontractors MEF Associates, Branch Associates, and Decision Information Resources (DIR), Inc. are conducting the Subsidized and Transitional Employment Demonstration.]