CTA is the next generation ground-based observatory for gamma-ray astronomy at very-high energies in the range from 30 GeV to 300 TeV. CTA’s detection of high-energy gamma rays is based on the imaging air Cherenkov technique (see How CTA Works). Three classes of telescope types are required to cover the full CTA energy range (20 GeV to 300 TeV). For its core energy range (100 GeV to 10 TeV), CTA is planning 40 Medium-Size Telescopes (MSTs). Eight Large-Size Telescopes (LSTs) and 70 Small-Size Telescopes (SSTs) are planned to extend the energy range below 100 GeV and above 10 TeV.