Ultrasound Localization Microscopy (ULM) is an ultrasound imaging technique that relies on the acoustic response of sub-wavelength ultrasound scatterers to map the microcirculation with an order of magnitude increase in resolution as compared to conventional ultrasound imaging.Initially demonstrated in vitro, ULM has matured and sees implementation in vivo for vascular imaging of organs or tumors in both animal models and humans. The performance of localization algorithms greatly defines the quality of vascular mapping. Here, we compiled and implemented a collection of ultrasound localization algorithms and devised three in silico and in vivo datasets to compare their performance through 11 metrics. We also present two novel algorithms designed to increase speed and overall performance. By providing a comprehensive open package to perform ULM that includes localization algorithms, the datasets used, and the evaluation metrics, we aim to equip researchers with a tool to identify the optimal localization algorithm for their 2 application, benchmark their own software and enhance the overall quality of their ULM images while uncovering the algorithms' own limits. MainThe circulatory system carries the essential nutrients of life to cells in the body. It forms a 100,000 kilometer-long network composed of centimeter-wide arteries down to capillaries that are a few micrometers in diameter at most. The study of the vascular system is essential for both the diagnosis and treatment of cardiovascular diseases, cancer, diabetes, stroke, or organ dysfunction.Due to its diversity of scale, imaging the vasculature is a daunting task and few techniques are capable of measuring micro-hemodynamics deep in the human body.Ultrasound imaging is extensively used in medical practice as a non-invasive tool that provides soft-tissue diagnosis, prognosis, or guides interventions. Using the Doppler effect, it can also measure blood flow in real-time. With the advent of plane wave techniques 1 , ultrasound has reached frame rates up to 20 kHz making it possible to observe and measure fast occurring changes 1 such as functional changes in the brain 2 , as well as increase sensitivity to blood flow that allows more accurate filtering 3,4 . To increase blood's contrast, micrometric gas microbubbles can be intravenously injected in vivo. Contrast-Enhanced Ultrasound (CEUS) is mostly used for perfusion studies and cardiac imaging 5 .Because conventional ultrasound imaging, Doppler, and contrast-enhanced ultrasound all rely on the propagation of sound waves, ultrasound imaging is largely limited in resolution by diffraction.Recently, Ultrasound Localization Microscopy (ULM) has broken that limit by isolating a small number of microbubbles as subwavelength sources in each image and localizing them with micrometric precision [6][7][8] . Similar to PALM (PhotoActivated Localization Microscopy), it uses

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