It is well-documented that there exists ethnic discrimination in the regular housing market in European and US cities. However, the existing literature has so far neglected the informal market for shared housing. We use a field experiment to investigate ethnic discrimination in this market. We sent fictitious inquiries with a randomly assigned name signaling a British, Eastern-European, Indian, African, or Arabic/Muslim background to more than 5,000 room advertisers in the Greater London Area. Our main finding is that ethnic discrimination is widespread. We also find that the degree of discrimination depends on the applicant’s occupation and the ethnic residential concentration.