With the spectacular development in radio and MEMS technologies,having sensor nodes capable of tuning efficiently their frequencyover different channels is more and more straightforward. For instance, TelosBmotes can communicate on multiple frequencies as specified in the802.15.4 standard. This reality has given birth to multichannelcommunication paradigm in Wireless Sensor Networks (WSN). Obviously,multichannel communication mitigates interferences, jamming andcongestion, whereas it brings also challenging issues. Thus, in thispaper, we are motivated to draw a picture of multichannel assignmentprotocols in WSNs. After having identified the reasons of resortingto multichannel communication paradigm in WSNs and the specificissues that should be tackled, we propose a classification ofmultichannel assignment protocols, pointing out different channelselection policies, channel assignment categories and channelassignment methods. We conclude by a recapitulative tableincluding many examples of existing multichannel protocols designedfor WSNs and point out promising research directions.