  We develop an effective field theory of a generic massive particle of any
spin and, as an example, apply this to study higher-spin dark matter (DM). Our
formalism does not introduce unphysical degrees of freedom, thus avoiding the
potential inconsistencies that may appear in other field-theoretical
descriptions of higher spin. Being a useful reformulation of the Weinberg's
original idea, the proposed effective field theory allows for consistent
computations of physical observables for general-spin particles, although it
does not admit a Lagrangian description. As a specific realization, we explore
the phenomenology of a general-spin singlet with $\mathbb{Z}_2$-symmetric Higgs
portal couplings, a setup which automatically arises for high spin, and show
that higher spin particles with masses above $O(10)\,\mathrm{TeV}$ can be
viable thermally-produced DM candidates. Most importantly, if the general-spin
DM has purely parity-odd couplings, it naturally avoids all DM direct detection
bounds, in which case its mass can lie below the electroweak scale. Our
formalism reproduces the existing results for low-spin DM, and allows one to
develop consistent higher-spin particle physics phenomenology for high- and
low-energy experiments and cosmology.
