A new class of superconducting magnets based on high temperature superconductors (HTS) has been envisioned to likely enable a paradigm shift in design and operation of particle colliders, energy systems, and medical devices. For example, HTS conductors can be used to construct powerful magnets that generate fields above 20 Tesla for the next generation of accelerators including a 4 TeV muon collider, or magnets working at >30 Kelvin in off-shore wind generators. Recent years have seen the emergence of several high-field superconductors, particularly Bi2Sr2CaCu2Ox, a high-temperature superconductor that has magnetic field upper limits surpassing 100 Tesla at 4.2 K and can be fabricated into a multifilamentary round wire. This talk will describe experiments and new technologies developed at Fermilab and U.S. HEP collaborations that have not only led to significant improvements in the critical current density (Jc) of Bi2Sr2CaCu2Ox, but have elucidated key mechanisms limiting the current flow. These works have steadily transformed Bi2Sr2CaCu2Ox into a practical magnet conductor. This talk will also discuss key engineering issues of using Bi2Sr2CaCu2Ox as well as other high-temperature superconductors, whose conductor characteristics are much different from those of low temperature superconductors so that many new concepts and tools needed to be developed. In particular, the talk will discuss recent experiments on detecting a quench and protecting HTS magnets from catastrophic quench damages, an important issue that has to be resolved in order to usher in a new era of high-temperature superconducting magnets.