'''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
==Railway Line== ===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
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