以【yǐ】

以 has two jobs in written Chinese. Before a noun it means "with" or "by means of", naming the means, manner or basis of an action. Between two verb phrases it means "in order to".

以 + noun: with, by, at, as

The 以 phrase goes before the verb. It often frames a longer noun: 以…的速度 "at a speed of", 以…的方式 "by way of", 以…的身份 "as", in the capacity of.

以…出名 or 以…闻名 says what someone or something is known for.

Verb phrase + 以 + verb phrase: in order to

The second verb phrase is the purpose of the first, and both share a subject. 以 comes after the first verb phrase, so this use never opens a sentence. To put the purpose first, use 为了.

• × 以提高效率，我们要加强管理 → 为了提高效率，我们要加强管理

以…为… "take X as Y", 以便, 以免, 以来 and 以上 / 以下 each have their own entry.