  Particle colliders for high-energy physics have been in the forefront of
scientific discoveries for more than half a century. The accelerator technology
of the colliders has progressed immensely, while the beam energy, luminosity,
facility size, and cost have grown by several orders of magnitude. The method
of colliding beams has not fully exhausted its potential but has slowed down
considerably in its progress. This paper briefly reviews the colliding beam
method and the history of colliders, discusses the development of the method
over the last two decades in detail, and examines near-term collider projects
that are currently under development. The paper concludes with an attempt to
look beyond the current horizon and to find what paradigm changes are necessary
for breakthroughs in the field.
