While substantial research has explored the cognitive processes underlying deception (e.g., Vrij et al., 2008, Suchotzki et al., 2015), emotional processes remain largely unclear. This study aimed to disentangle the cognitive and emotional mechanisms involved in lying through a simultaneous investigation of both factors. We used an adapted version of the Sheffield Lie Test (Spence et al., 2001), in which participants (n=49) responded truthfully or deceptively to either neutral or mock crime-related questions, depending on block-specific instructions. After each block, participants rated how cognitively and emotionally demanding they experienced responding in the respective block. In line with our hypotheses, deceptive responses led to significantly longer reaction times and higher perceived cognitive and emotional load compared to truthful responses. Responses to mock crime-related questions also led to longer reaction times and higher perceived cognitive and emotional load than responses to neutral questions. Contrary to expectations, there was no significant interaction between question type and response instruction. Further analyses identified a range of specific cognitive (e.g., response inhibition, strategy selection) and emotional (e.g., nervousness, fear) processes that were more pronounced during deception that during truth-telling, collectively contributing to the increase in reaction time during deception. These findings underscore the essential role of both cognitive and emotional processes in deception and provide insights into the further specification of these processes.