Much of the Berber family approximates to a dialect continuum, and the relationship between its members is close enough that it has often been considered as a single language. This has tended to distract from the concomitant existence of tree-like splits within Berber, first noted a century ago but clarified more recently. As a result, the study of intra-Berber diffusion has been largely neglected, even though the existence of dialect continua implies diffusion. This article lays out the principal models proposed for the sub-classification of Berber, a field which has advanced significantly in recent decades, along with their historical implications. It then presents two very different case studies-the Blida Atlas (Algeria), and Zenaga (Mauritania)-demonstrating that intra-Berber contact can sometimes be detected, even in quite basic vocabulary, and that the results fit well with the history implied by extra-linguistic data. Avenues for further research are suggested.