In this thesis, I investigate idiom processing from two angles through three different studies. First, I approached idiom processing from a constraint-based perspective. According to this view, not all idioms are alike: they can differ regarding lexical, and linguistic characteristics, such as their level of familiarity. In this first study, I investigated the underlying processes during the comprehension of idioms with different characteristics. I used the Event Related Potential (ERP) technique, which has high temporal resolution, to investigate this issue. I provided evidence that idioms' characteristics impact their processing. More specifically, idioms which are more familiar to language users (i.e., the ones that are encountered more frequently) showed processing facilitation compared to less familiar idioms. Also, idioms with plausible literal interpretation showed processing advantages over idioms which are less likely to be interpreted literally. The second aim of the current thesis was to investigate idiom processing from an embodied account of language processing. According to this view, various sources of information (including linguistic, affective, and sensory-motor) are available and used during the comprehension of language. While, this view has become popular in many language processing studies, studies of idiom processing are still at the beginning of this journey. To be able to investigate idiom processing while considering the role of affective and sensory-motor factors, we require access to norming data. In the second (descriptive) study, I conducted a large-scale survey and collected measures of valence, arousal, concreteness, and imageability for a set of English idioms, by both native speakers of English and proficient second language speakers. In the last study, I explored how the emotional status of idioms and their concreteness contributes to their processing, and whether this contribution is modulated by idiom familiarity. We found that the impact of non-linguistic sources of information (affective and sensory-motor) is determined by idiom familiarity, such that low familiar and high familiar idioms show different behaviour where these factors are concerned. For highly familiar idioms, behaviour aligns with the findings on word processing: for example, idioms with more positive valence showed facilitative processing. Unlike highly familiar idioms, valence had an inhibitory impact on idioms with low familiarity level, such that greater valence increased the reading time.