This paper is concerned with selection of seeds by animals that search for and respond to seeds as individual items. It also considers mutualistic frugivory. Techniques and results of studies of frequency-dependent selection of food are discussed. Frequency-dependent selection may be constant in direction, only its strength varying with the frequencies of the various types of food available, or it may vary in direction according to frequency (apostatic selection). Frequency-dependent selection is common, though only some experiments show apostatic selection. Selective behaviour is often variable within a single experiment, making replication important. Selection tends to be anti-apostatic when the prey are crowded. In principle, frequency-dependent seed-predation could be important in enhancing or reducing vegetational diversity and within-species variation - and in causing the convergence or divergence in appearance of coexisting species. I discuss the evidence for