A skyline is the outline of buildings and structures you see against the sky when you look at a city from a distance. When you approach New York City and spot the tall buildings creating a jagged line across the horizon, you're seeing its famous skyline. Chicago's skyline looks different from San Francisco's, and London's skyline looks different from Dubai's, because each city has its own unique collection of towers, skyscrapers, and landmarks.

Before cities had tall buildings, their skylines were much flatter, punctuated mainly by church steeples or clock towers. Today's dramatic skylines, filled with glass and steel skyscrapers, are mostly a 20th-century invention.

You might hear someone say they love the mountain skyline from their bedroom window, or talk about how construction cranes are changing the city's skyline. Artists and photographers often feature skylines in their work because these distinctive outlines can capture a city's personality in a single image. The Empire State Building, the Eiffel Tower, and the Space Needle all help define their cities' skylines and make them instantly recognizable.