The Royal Society's Philosophical Transactions is the oldest surviving scientific journal in the world. In connection with its 350th anniversary in 2015, the AHRC funded a collaborative project between the University of St Andrews and the Royal Society. It had three aims: 1) to enable researchers to investigate the editorial and commercial history of scientific journal publishing; 2) to help the Society celebrate its significant anniversary; and 3) find ways for the historical perspective to inform public debate about the future of scholarly publishing. The research speaks to academic communities in the history of science, the history of publishing and economic history; as well as to stakeholders in the worlds of research libraries, publishing, learned societies and higher education policy. The origins of the Philosophical Transactions, and its function in the newly-founded Royal Society in Restoration England had already been studied by historians of early modern science. So too, the literary qualities of its articles had been extensively analysed by scholars interested in the rhetoric of science; and its citation patterns have been studied by sociologists of science as evidence of the functioning of past communities of scientists. The unique selling points of our project are our focus on telling the 'big picture' story over a full 350 years; and our emphasis upon the historical archival materials that allow us to investigate the commercial, economic and editorial practices which lie behind the published pages. We argue that, while the Transactions was undoubtedly of foundational importance to the development of science communication, it has never at one time united all the attributes of the modern scientific journal. The story we have revealed is not the biography of a single entity, but a history of repeated transformation and reinvention, reaction and reform, crisis and complacency. By following the Transactions through its many lives, we can uncover the sheer complexity of the processes by which an innovation became an institution and the historical burdens of institutional status. We tell the story of the evolution of the Transactions from a speculative commercial sideline (a scientific news-sheet put out by an entrepreneurial scholar) in the late seventeenth century, to the official publication and chief business of one of the world's oldest and most influential learned societies, two centuries later; how those 'transactions' developed from reports of society meetings to a modern scientific journal, and its peculiar twenty-first century position as both one scientific journal among thousands and a unique historical survival. Along the way, we reveal the deep genealogy of the editorial peer review process _ the central pillar of modern scientific practice _ and the gulf between the pressures that called it into being in the early nineteenth century and the claims made for it in the late twentieth and early twenty-first. The story of the Philosophical Transactions embodies the tension between the claims of the individual researcher and the wider scientific enterprise, but also reveals a surprisingly long-standing philanthropic commitment to the circulation of knowledge, that puts the commercial ambitions of modern scientific journal publishers into perspective. By touching on issues at the heart of the knowledge-based economy, it has substantial contemporary relevance to a wide audience of policy makers, educators and campaigners.