Objective To develop a portable microscope capable of interrogating the microcirculation in vivo with multiple contrasts over multiple spatial scales. Methods We used state-of-the-art 3D printing and optics design techniques to fabricate a miniature microscope the size of a US quarter (Fig. 1 a, b)1. It weights 9g and acquires images via three optical contrasts: intrinsic optical signals (IOS)2, laser speckle contrast (LSC)3 and fluorescence (FL). The IOS channel, which relies on light absorption by red blood cell (RBC) bound hemoglobin (HbT), can be used to visualize microvascular morphology, while the LSC channel enables observing blood flow levels by using the orderly flow of RBCs along vessels as a contrast agent. The FL channel can be used for arterio-venous discrimination via the arrival times of an intravenously (iv) injected fluorescent dye (e.g. FITC-Dextran, 70 kDa). The microscope can acquire images at 15 frames per second over a 3x3 mm2 field of view (FoV) at 5 µm resolution. We also designed an adaptor which enhances the resolution tenfold to 0.5 µm. It is operated via USB connections to a laptop, and is portable (Fig. 1c), making it convenient for imaging the microcirculation in a range of preclinical applications. Results We demonstrated the utility of our microscope by using it to interrogate the structure and function of the murine brain and ear microcirculation at different spatial scales. Figs. 1d, e show maps of microvascular morphology and blood flow in a portion of the murine brain under ketamine anesthesia at 5 µm resolution. Fig. 1f shows the map of arrival times of the iv injected fluorescent dye. Dark blue regions corresponding to arrival times less than 0.5 s were used to identify arteries. Figs. 1g, h show plots of changes in HbT (i.e. cerebral blood volume) and cerebral blood flow (CBF) corresponding to an artery and vein (boxes marked “A” and “V” in Fig. 1d) over 3 hours while the animal recovers from anesthesia. Here, the arterial and venous time courses illustrate contrasting flow-volume relationships that indicate the varying systemic effects of anesthesia on components of the microcirculation. Fig 2a shows the microscope with its high-magnification adaptor, while Fig. 2b illustrates the exquisite microvascular details revealed with the adaptor in contrast to images acquired without it. Here, the FL channel was used in conjunction with an iv injected dye to enhance microvascular contrast. One could also “stitch” together these high-resolution images to create a mosaic with wider coverage (Fig. 2c). Since individual RBCs were discernable in these high-resolution images (Fig. 2d), we successfully employed RBC tracking to characterize cellular-scale flow dynamics within the microcirculation (Fig. 2e). Conclusion The multicontrast and multiscale imaging capabilities of our microscope will enable investigators to comprehensively interrogate the structure and function of microcirculation in diverse organ sites and preclinical disease models. Its design and portability enables imaging of unanesthetized animals, convenient usage, and fosters collaborations.