This paper studies the interlinkages among Bitcoin and seven Bitcoin forks, which share proof-of-work. To this end, I propose two volatility indexes and one correlation index based on the estimation of three multivariate GARCH models. This study finds that the contribution of the Bitcoin-fork volatility to the market volatility is stronger in the first two months after the occurrence of a fork, and low thereafter. Furthermore, the correlation of Bitcoin with four Bitcoin forks is negative or low during high-volatility times and highly positive during low-volatility times. The other three Bitcoin forks do not show this correlation pattern.