In 1902, a contributor to Popular Science affirmed that “The era of the amateur scientist is passing; science must now be advanced by the professional expert.” Throughout the twentieth century, amateurs have been increasingly excluded from the production of scientific knowledge. But since the 1990s, under the banner of “citizen science”, a growing number of initiatives have involved, once again, amateurs in science, with the goal of democratizing science, promoting scientific literacy, and solving big data problems. The creation of SETI@home at UC Berkeley in 1998 embodied all these aims. Within six month, it had attracted more than one million participants analyzing radio signals from space on their personal computer searching for signs of extraterrestrial life. The initiators of the project and the media constructed the image of the participant along the lines of an imagined amateur scientist making discoveries outside of scientific institutions, while contributing to the making of a global scientific citizenship. Infused by libertarian, countercultural, and cyber-utopian ideals, SETI@home seemed to capture the scientific aspirations of a new generation. But the tens of thousands of online biographical sketches left by the participants present a more nuanced picture. These traces offer a unique window into the self-fashioning of the participants into different kinds of “amateurs”, “volunteers”, and “hobbyists” with various views about professional science and its place in society. These sources helps us better understand the recent reconfigurations of the amateur scientist and, more generally, the struggles over the legitimacy of professional expertise.