The fundamental purpose of this thesis was to determine how effective is the theory of planned behaviour (TPB) to predict and explain shopping for embarrassing products in single and multi-channel. This is important because multi-channel consumers buy more, the question is why (Neslin, Grewal et al. 2006). The question was answered by comparing consumer behaviour in three different channels: drugstore, internet and multi-channel. The Theory of Planned Behaviour (TPB) has been successful to predict intentions for a wide variety of products and behaviours. However, little is known about how effective it is when the behaviour under study is influenced by the emotion of embarrassment. Similarly, the TPB is parsimonious and has a good predictive power; nevertheless, this thesis identified that the TPB could be more effective if it considered: (1) the role of positive and negative emotions (2) other determinants of choice like personality and demographics (3) variables that are useful to make marketing decisions like the synergistic effect of brands, retailers and channels (4) variables that explain consumer response like approach and avoidance. To provide a comprehensive theoretical framework that is able to understand single and multi-channel, this thesis integrated the TPB within the Stimulus-Organism-Response (S-O-R) framework. To evaluate the proposed model, the study used a context and target product that resonated with the theory: the purchase of Regaine (a hair loss product that is embarrassing to buy) in Boots (a well-known UK. multi-channel drugstore). The embarrassing nature of Regaine created differences in the importance that variables play in each channel. The results were analysed using partial least squares structural equation modelling (PLS-SEM) and the three shopping environments were compared using multi-group analysis (MGA). The effectiveness of the TPB was improved. The variance explained (R² to intention) was 73 percent for the drugstore, 67 percent for the internet and 54 percent for multi-channel. However, subjective norm (SN) was the only factor that achieved significance for the three shopping environments. Personality and demographic factors had a low but significant moderating effect on intention. This thesis built on a series of contributions in different areas, such as the TPB, attitudes, subjective norm, perceived behavioural control, embarrassing products, multi-channel, marketing, emotions, personality and demographics. Future research should expand this thesis to other embarrassing products, industries and social media settings.