Line 21

Line 21 may refer to:

Closed Captioning

 * EIA-608, a standard for closed captioning for NTSC TV broadcast, also known as "line 21 captions"

Telecommunications
Line 21, a Hungarian telecommunications company Vodafone Hungary

In operation

 * Line 21 (Guangzhou Metro), a metro line of the Guangzhou Metro in China
 * Line 21 (Zürich), Switzerland
 * Yangluo Line, a metro line of the Wuhan Metro in China

Under Planning

 * Line 21 (São Paulo Metro), a future metro line of the São Paulo metro
 * Line 21 (Shanghai Metro), a future metro line of Shanghai Metro