Massive galaxies reside in the densest and most evolved regions of the Universe, yet we are only beginning to understand their formation history. Once thought to be relics of a much earlier epoch, the most massive local galaxies are red and dead ellipticals, with little ongoing star formation or organized rotation. In the last decade, observations of their assumed progenitors have demonstrated that the evolutionary histories of massive galaxies have been far from static. Instead, billions of years ago, massive galaxies were morphologically different: compact, possibly with more disk-like structures, and on-going star formation. The details of this observed evolution can place constraints on the physical processes that have driven massive galaxy evolution through cosmic time. I will discuss on-going observational studies of the structure, dynamics, and compositions of massive high-redshift galaxies. Specifically, I will highlight preliminary results from the LEGA-C spectroscopic survey of 0.6 < z < 1 massive galaxies. Finally, I will outline prospects for further understanding of the history of these intriguing objects with next generation observatories and instruments.