Online trading has now become the prevalent form of stock market investing. With a largepercentage of investors online, understanding how they gather, use and share information is ofmajor interest to service providers, regulators, researchers and to investors themselves. Previousstudies have examined the adoption of online investing, the impact of online stock forums onmarkets and the information content of stock forums. A relatively limited number of studieshave investigated the information seeking practices of online investors. This study sought adeeper understanding of what drives the information behaviour of online investors.This research reports on a qualitative study that interviewed 26 online investors about theirinformation practices and social networks. The interview transcripts were analysed using aGrounded Theory methodology and the research process was also influenced by aspects ofMulti-Grounded Theory. A new Theory of Online Investor Information Behaviour has beendeveloped as a result of the analysis.The theory introduces the concept of an Investment Persona – a role that an investor takes on –that has a large impact on their information seeking behaviour. Investors may take on multiplePersonas simultaneously. A number of distinct Persona types were identified in the study: LongTerm Investor, Income Generator, Trader, Speculator, Venture Capitalist, Novice and Gambler.The theory also includes a model of the Stock Investing Information Process, which includes thetasks: Idea Generation, Stock Selection, Company Research, Buy, Monitor and Sell. Whileinformation practices are incredibly diverse in the early stages of the investment process, thelater stages tend to be more homogenous.A core aspect of the theory is the concept of an Information Lens. Rather than using allinformation sources and social networks at all times, investors look through an Information Lens,seeing only a small subset of their information world at any particular time. The InformationLens is highly dynamic and is shaped by the current Persona and the task at hand.The bidirectional relationship between the investor and the information world is also considered.The information environment itself can influence the investor and change their behaviour, byenabling new strategies that were not previously possible, or potentially threatening the investorwith information overload. Online technologies can also enhance the investing experience andmake it more interesting and exciting.