The ECP Co-design Center for Particle Applications (CoPA) is addressing the challenges for particle-based applications to run on upcoming exascale computing architectures. This scope is partitioned into four “sub-motifs”: short-range particle-particle interactions (e.g., those which often dominate molecular dynamics (MD) and smoothed particle hydrodynamics (SPH) methods), long-range particle-particle (e.g., electrostatic and gravitational) interactions, particle-in-cell (PIC) methods, and linear-scaling electronic structure and quantum molecular dynamics (QMD) algorithms. Our crosscutting co-designed technologies fall into two types, proxy applications (or “apps”) and libraries. Proxy apps are tools to explore algorithms, data structures/layouts, optimizations, etc., and the associated tradeoffs on different architectures.