Chaki (茶器) is a Japanese term that literally means "tea implement". In the vocabulary of Japanese tea ceremony, it broadly means (1) any implement used in the practice of chanoyu, and more narrowly means (2) the caddy for the powdered green tea (matcha) used in the tea-making procedures, although usually this implies (3) the caddies used in the procedures for making thin tea (usucha). In this article, the term applies to definition 2.

The caddies generally referred to as chaki are relatively small lidded containers, and are not storage vessels. In preparing to perform a tea-making procedure (temae), the host carefully selects the caddy for the matcha that will be used, and, as an important part of the preparations, neatly places the matcha into it. The chaki is chosen to harmonize with the other equipment used for the occasion, and the chaki is among the items the guests pay particular attention to.

Chaki are classified both by material and shape, as well as by the type of tea preparation (thin tea or thick tea) for which they are used.

Chaki can be divided into two broad categories: those made of ceramic, and those made of wood or bamboo. Normally, ceramic chaki are for use in the procedures to make thick tea (koicha), and are called chaire (茶入, "tea container")(ja) or koicha-ki (濃茶器;　"implement for thick tea").

Wood or bamboo chaki normally are for use in the procedures to make thin tea, and are also called usucha-ki (薄茶器), "implement for thin tea," often abbreviated usuki). Commonly these are of the shape category called natsume (棗, "jujube"), and so usucha-ki in general tend to be loosely referred to as natsume.

Both chaire and natsume are further classified according to country of origin, materials and shape, and in some cases by potter or, in special cases, a name given to the object.

Broadly speaking, an usucha-ki is a wooden vessel with a lid, designed to hold powdered tea for making thin tea. Traditionally, usucha-ki are hand-carved from wood or bamboo, and usually are lacquered. They may also feature designs painted, applied, or carved into them, using for instance the maki-e or raden techniques. Today, cheaper, mass-produced plastic usucha-ki are also available.

The name natsume comes from the natsume or jujube fruit, which some usucha-ki are said to resemble. Strictly speaking, the word natsume should only be used to refer to vessels which have a slightly convex top and body that gradually narrows toward the base, but in practice any usucha-ki may be referred to as a natsume.