  This paper reviews the status of high temperature superconductors for high
field magnets for future devices such as a high energy LHC or a muon collider.
Some of the primary challenges faced for the implementation of systems are
discussed. Two conductor technologies, Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ and
YBa$_2$Cu$_3$O$_{7-\delta}$, have emerged as high field conductor options, but
their relative advantages and disadvantages for high field magnets are quite
different. These are reviewed from an engineering perspective, including coil
manufacturing, electromechanical behaviour and quench behaviour. Lastly, the
important roles of "system pull" upon conductor and magnet technology
development, and of interactions between the materials and magnet communities
for accelerating development, are discussed.
