Reflectors can be used to concentrate direct solar radiation onto an absorber so that it can produce steam either directly or indirectly. This is then used as industrial process steam or converted into electricity by a power plant unit. A variety of collector technologies are used and developed for this process: Parabolic trough collectors are the most widespread, having been successfully employed in solar thermal power plants since the 1980s. Meanwhile, solar power towers that focus the sun’s rays onto a point on the tower generally achieve higher temperatures. By using molten salt as their heat-transfer medium, they promise greater efficiency, as this substance is directly stored once hot. Linear Fresnel collectors that generate steam directly are also able to reach temperatures of up to 500 °C but offer the added advantages of more efficient land use and having lower component costs. Collectors of various sizes are developed and enhanced for different areas of application, from small rooftop installations in the kW range, solar cooling systems and process steam generation to solar thermal power plants in the 100 MW range. In addition to considering costs, the geometric arrangement and optics, as well as thermal losses and temperatures, must be taken into account when optimizing collectors. To achieve this, we use optical and thermal simulation tools, and combine theoretical models with measurements taken from components and collectors.