Giant-screen, 70mm movie theatres started showing up in educational venues in the 1970s, and in cinema multiplexes in the 1990s. The benefits were state-of-the-art appeal via super-high-res film projection and immersive screen size. Today, more than 25% of such theatres are in multiplexes, which favor 3D systems. Most of the rest are in nonprofit venues such as science museums. The multiplexes and the nonprofits have vastly different missions and often present widely different content. But they are fellows in today’s struggle to maintain audience numbers against the rising tide of in-home entertainment.