This paper argues that the citation of foreign legal sources in judicial decisions is not essentially a free-standing justification. Rather it gives additional support to arguments that can be based on existing domestic legal sources by showing that these illustrate a principle or value shared by a number of other legal systems. Legal development does not work simply by reformulating the rules by borrowing words or rules from other jurisdictions. Law develops by re-interpreting existing principles and rules in the current context of the legal system as a whole. The article draws on the work of Markesinis and Waldron and on the European Legal Development project which the author led with Professor David Ibbetson.