Bitcoin and ethereum (ether) are cryptocurrencies that can be purchased directly on a cryptocurrency exchange. You could also invest in both via investment trusts, such as those offered by Grayscale, but they have stiff fees and minimum investment requirements. Another way to invest is through derivatives such as bitcoin or ether futures and options. You could also invest in bitcoin by purchasing bitcoin futures exchange traded funds (ETFs) or buying stocks of companies such as Riot Blockchain, that are involved in bitcoin mining.