Castle Island Ventures is a venture capital firm focused exclusively on public blockchains. Based in Cambridge, Massachusetts, they invest in infrastructure and application companies that enable transformative protocols to power services for the next billion users. The firm specializes in seed and early-stage investments, with a particular emphasis on the cryptocurrency and blockchain sectors.

Notable portfolio companies include BlockFi, Coin Metrics, and TRM Labs. Castle Island Ventures believes that permissionless blockchains represent a new form of politico-economic institution that will fundamentally alter market structures. The firm's investment philosophy centers on supporting innovative projects that leverage blockchain technology to create disruptive solutions across various industries.