This paper reviews the main research that has been conducted on the role of orthographic neighbourhood in visual word recognition. We focus here on the traditionally defined neighbourhood, that is corresponding to the set of words of the same length sharing all but one letter with the stimulus. Two major theoretical frameworks, namely the activation verification and the interactive activation models, assume that orthographic neighbours are activated when a written word is presented. Predictions formulated by both models for words and pseudowords on the effects of neighbourhood size (N), neighbourhood frequency (NF), and neighbourhood distribution (P), are examined in order to assess the plausibility of serial versus interactive processes. Findings from 27 empirical studies including more than 80 experiments suggest that neighbourhood effects depend on the neighbourhood indexes (N, NF, and P), on the particular tasks (lexical decision, naming, semantic categorization, perceptual identification, and reading), and on the languages (English, French, Spanish, and Dutch) that are used. The results for words can be summarized as follows: (1) In the lexical decision task, the N effect is facilitatory. The NF effect is rather inhibitory, particularly in French and Spanish experiments. The P effect is rather inhibitory in English studies, whereas the P effect for higher frequency neighbours is facilitatory in French. (2) In the perceptual identification task with a single identification response, N and NF effects are inhibitory whatever the language. (3) In the naming task, N and NF effects are facilitatory whatever the language. (4) In the semantic categorization task, an interaction effect between N and NF is found in both English and Spanish. (5) In eye movement studies, the NF effect is inhibitory in both English and French. The issue of lexical versus task-specific processes underlying neighbourhood effects in lexical identification tasks is also examined. On the whole, facilitatory N effects are usually attributed to nonlexical processes of the lexical decision task and of the naming task, whereas inhibitory neighbourhood frequency effects are usually attributed to lexical processes, at least in lexical-decision experiments and in eye-movement studies on normal reading. The distribution of higher frequency neighbours which is found to have a facilitatory effect on French words in lexical-decision experiments can be attributed to lexical processes in the interactive activation framework. The theoretical implications of the data are discussed in light of the original activation verification and interactive activation models and in recently extended versions of these models. We conclude that the lexical inhibition hypothesis which is central in the interactive activation framework is the most appropriate to account for the role of orthographic neighbourhoods in visual word recognition.