This paper presents the MESA Isochrones and Stellar Tracks (MIST) project, a new set of stellar evolutionary tracks and isochrones computed using the MESA stellar evolution code. The models cover a wide range of ages (5 ≤ log(Age)[yr] ≤ 10.3), masses (0.1 ≤ M/M☉ ≤ 300), and metallicities (−2.0 ≤ [Z/H] ≤ 0.5), with solar-scaled abundance ratios. The models are self-consistently evolved from the pre-main sequence (PMS) to the end of hydrogen burning, white dwarf cooling, or the end of carbon burning, depending on the initial mass. A grid of models is also provided for metallicities −4.0 ≤ [Z/H] < −2.0, evolved from the PMS to the end of core helium burning. The models are compared with observational constraints and existing models in the literature. The evolutionary tracks and isochrones can be downloaded from the project website. The MESA code is a flexible, open-source 1D stellar evolution package that allows for the self-consistent modeling of different types of stars to advanced evolutionary stages. The code includes a modular structure that enables the implementation of various physical processes, such as the equation of state, opacities, nuclear network, boundary conditions, diffusion, rotation, and mixing processes. The models are calibrated against the properties of the Sun and include bolometric corrections. The paper discusses the adopted physics, including the treatment of abundances, microphysics, and the implementation of various mixing processes. The models are compared with observational data for low-mass and high-mass stars, and the paper concludes with a discussion of caveats and future work.This paper presents the MESA Isochrones and Stellar Tracks (MIST) project, a new set of stellar evolutionary tracks and isochrones computed using the MESA stellar evolution code. The models cover a wide range of ages (5 ≤ log(Age)[yr] ≤ 10.3), masses (0.1 ≤ M/M☉ ≤ 300), and metallicities (−2.0 ≤ [Z/H] ≤ 0.5), with solar-scaled abundance ratios. The models are self-consistently evolved from the pre-main sequence (PMS) to the end of hydrogen burning, white dwarf cooling, or the end of carbon burning, depending on the initial mass. A grid of models is also provided for metallicities −4.0 ≤ [Z/H] < −2.0, evolved from the PMS to the end of core helium burning. The models are compared with observational constraints and existing models in the literature. The evolutionary tracks and isochrones can be downloaded from the project website. The MESA code is a flexible, open-source 1D stellar evolution package that allows for the self-consistent modeling of different types of stars to advanced evolutionary stages. The code includes a modular structure that enables the implementation of various physical processes, such as the equation of state, opacities, nuclear network, boundary conditions, diffusion, rotation, and mixing processes. The models are calibrated against the properties of the Sun and include bolometric corrections. The paper discusses the adopted physics, including the treatment of abundances, microphysics, and the implementation of various mixing processes. The models are compared with observational data for low-mass and high-mass stars, and the paper concludes with a discussion of caveats and future work.