Due to the unsuitability of bench-top imaging for tasks that require unrestrained movement we developed miniature two-photon microscopes that can be carried on the head of freely moving animals. The performance and reliability of two-photon miniscopes (MINI2P) are validated by recordings of spatially tuned neurons in three brain regions and in three behavioral assays. The new technique permits large-scale and high-resolution calcium imaging in freely-moving mice and opens the door to investigate brain functions during animal`s most natural behaviors. Current limitations and future developments will also be discussed.