Anonymous trading is the norm in today's financial markets but there are a few exceptions. We study one such case, the OMX Nordic Exchanges (Stockholm, Helsinki, Copenhagen, and Reykjavik) that have traditionally been more transparent than most other markets. On June 2, 2008 OMX Nordic switched...

We report evidence that the presence of hidden liquidity is associated with greater liquidity in the order books, greater trading volume, and smaller price impact. Limit and market order submission behavior changes when hidden liquidity is present consistent with at least some traders being able...