When to Kern

The objective of kerning is to achieve the appearance of equal spacing on either side of each character. Thankfully, the majority of your kerning needs are addressed by InDesign's automatic kerning methods, of which there are two kinds: Metrics and Optical. Either method adequately handles kerning at small type sizes, so you don't need to drive yourself crazy finding every instance of troublesome kerning pairs and manually adjusting their spacing. Regardless of the method you use, you can always add manual kerning as needed.

Figure 5.1. Why we kern. (A) No kerning, (B) Metrics Kerning, (C) Optical Kerning, (D) Optical Kerning with additional manual kerning.

Figure 5.2. Basic Character Formats.

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Automatic kerning can be applied locally by selecting a range of text, then choosing Metrics or Optical from the Control palette (or the Character palette), but you're better off choosing your automatic kerning method as part of a style sheet definition.