Present status and future perspectives of the particle methods which have been developed to be applied to various problems in fluid dynamics. The concept of the particle methods, Lagrangian description of the calculation points without mesh, was presented at the early stage in the history of computational fluid dynamics. Application to incompressible flows with free surfaces was achieved by a fully explicit algorithm assuming weakly compressible approach and a semi-implicit algorithm imposing the incompressibility condition. As spatial discretization schemes, smoothing using the kernel function is formulated in Smoothed Particle Hydrodynamics (SPH) [1,2] and a weighted difference is employed in Moving Particle Semi-implicit (MPS) method [3]. To date, advanced techniques have been developed: wall boundary conditions, multi-resolution techniques, surface tension models, enhancing numerical stability, etc. Higher-order spatial discretization schemes are derived from Taylor expansion and accuracy of the particle methods is substantially improved. Formulation based on analytical mechanics combined with symplectic schemes ensures conservation of kinetic energy. These approaches are useful in a wide range of applications. Calculation examples are provided to show the utility of the particle methods: free surface flows, tsunami inundation, rain water flow, fluid-rigid body interaction, non-Newtonian fluid flow, etc. REFERENCES [1] L. B. Lucy, A numerical approach to the testing of the fission hypothesis, Astronomical J. 82, 1013-1024 (1977). [2] R. A. Gingold and J. J. Monaghan, Smoothed Particle Hydrodynamics: theory and application to non-spherical stars, Mon. Not. R. Astr. Soc. 181, 375-389 (1977). [3] S. Koshizuka and Y. Oka, Moving-particle semi-implicit method for fragmentation of incompressible fluid, Nucl. Sci. Eng. 123, 421-434 (1996).