This article analyses the information system that supported London's first financial market. It reveals a significant and advanced system of information exchange, but also shows that early modern investors still had to negotiate many barriers in their search for full and accurate data. As a result a multi-tiered market emerged in which 'insiders' could command superior access to information, while 'outsiders', notably inactive, provincial or female investors, had to be content with older and less reliable information. This had both negative and positive consequences for London's financial market. From a negative perspective it offered opportunities to speculators and, in particular, allowed them to combine and manipulate the prices of some smaller joint stock companies. But the larger companies, like the East India Company and the Bank of England, because they attracted many riskaverse investors who were not bombarded with information and therefore did not change their investment strategies with every whim, became more difficult to manipulate. In consequence they achieved a measure of stability that ensured their longevity.