MIMMS (Modular In vivo Multiphoton Microscopy System) is a modular platform for performing two-photon laser scanning microscopy (TPLSM) optimized for in vivo applications. The system generally uses the core parts of the Sutter MOM (moveable objective microscope) system to provide for 4 degrees of freedom (three linear and one rotational) of objective movement for in vivo experiments. These parts are purchased from Sutter. The mechanical backbone of this system is a movable, raised optical breadboard, providing a large area for affixing optical equipment associated with the microscope, including multiple scanners, beamshaping optics, photostimulation lasers, cameras, etc. The raised design also provides space for behavioral apparatus, and allows the entire microscope to move out of the way for easy 360 degree access to this working area. A modular approach was taken in designing the microscope components, with interchangeable systems for different laser scanning modalities, both moving (based on the Sutter MOM system) and fixed objective lens mounting, widefield conventional imaging, and high acceptance, non-descanned fluorescence detection.