The present invention relates to bicyclic heterocycles which are inhibitors of BET proteins such as BRD2, BRD3, BRD4, and BRD-t and are useful in the treatment of diseases such as cancer.Linvention concerne des hétérocycles bicycliques qui sont des inhibiteurs de protéines BET telles que BRD2, BRD3, BRD4 et BRD-t et sont utiles dans le traitement de maladies telles que le cancer.