Objective: Internet-delivered cognitive–behavioral therapy (ICBT) has been established as both efficacious and effective in reducing symptoms of social anxiety. However, most research has been conducted in controlled settings, and little is known regarding the utility of such programs in an open-access format. The present study examined the use, adherence, and effectiveness of Joyable, an open-access, Internet-delivered, coach-supported CBT-based intervention for social anxiety. Method: Participants were 3,384 registered users (Mage [SD] = 29.82 [7.89]; 54% male) that created an account between 2014 and 2016. Characteristics of use, factors related to attrition and adherence, and within-group outcomes were examined. The primary outcome measure was the Social Phobia Inventory. Results: On average, participants remained in the program for 81.02 days (SD = 60.50), during which they completed 12.14 activities (SD = 11.09) and 1.53 exposures (SD = 3.18). About half (57%) had contact with a coach. Full adherence to the program was achieved by 16% of participants, a rate higher than previously published open-access studies of ICBT. Social anxiety symptoms were significantly reduced for participants that engaged in the program, with medium within-group effects from baseline through the cognitive restructuring module (d = 0.63–0.76) and large effects from baseline through the exposure module (d = 1.40–1.83). Response rates were high (72%). Exposures and coach contact were significant predictors of retention and outcome. Conclusions: This open-access online CBT-based program is effective in reducing social anxiety symptoms and has the potential to extend Internet-based mental health services to socially anxious individuals unwilling or unable to seek face-to-face evidence-based therapy.