Background: While resources exist to address the needs of graduate medical trainees, online resources to assist trainees with specialty-specific professional development have not been fully developed or described in the past. The Hem-Onc Fellows Network (@HemOncFellows) is an online community for hematology-oncology trainees in all stages of training, including medical students, residents, fellows, and doctoral students. The network's goals are to provide professional development in hematology-oncology, create a community and safe space for hematology-oncology trainees, and amplify the voices and needs of trainees. Methods: The @HemOncFellows Twitter account was created in February of 2021. The hashtag #HOFellows was registered and certified with healthcare Symplur. The network hosts Twitter Spaces (TS) with guests every two weeks and distributes a newsletter. Fifteen TS were held between July 2021 and February 2022. For each TS, a specific topic of professional development was discussed. At least one content expert was invited to each TS to provide additional commentary. Demographics of TS participants and newsletter subscribers were gathered and qualitative and quantitative analysis was performed. Results: Since its inception, the Hem-Onc Fellows Network has grown to more than 2200 followers. Symplur has over 500 #HOFellows tweets from November of 2021 to early February of 2022. The network organized 15 TS: 14 in professional development topics and one meet-and-greet for new matched fellows in December. TS had an average of 41 participants per event. Most participants were United States-based but there were participants from 21 countries worldwide. Forty-eight participants attended three or more spaces, including 15 hem-onc fellows and 17 internal medicine residents. The newsletter has 48 subscribers. Conclusions: We demonstrate that implementing a trainee network on Twitter attracted participation and engagement from a diverse pool of trainees worldwide. TS represents a novel educational tool for engaging trainees and facilitating professional development.