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This paper focuses on spectrum handoffs in a cognitive radio network where secondary (unlisenced) users (i.e. cognitive radios) opportunistically use frequency channels as long as the aggregate interference caused at the primary (licensed) users does not exceed a certain threshold. When harmful interference is caused to a primary user, or when the quality of service perceived by a secondary user is not satisfactory, the secondary user has to initiate a spectrum handoff to quickly vacate the channel it is occupying. The proposal in this paper is a fuzzy-based approach able to make effective spectrum handoff decisions in a context characterized by uncertain, incomplete and heterogeneous information.