The 21st century world is characterized by globalization, optimization, high performance demands, and continuous acceleration of processes. Not surprisingly, stress has steadily become more prevalent over the past years and has become a permanent challenge for many of us. Still we are always expected to perform at our best, and an impairment of cognitive performance can be devastating, particularly in the professional world. This ubiquity in daily life of chronic stress, cognitive demands, and their potential interactions was the motivation for this dissertation. Among cognitive processes executive functioning (EF) are of particular interest, as they represent set of fundamental cognitive abilities for mastering daily life. More precisely, EF is described as higher-order cognitive processes that control and coordinate complex cognitive tasks (Diamond, 2013; Miyake et al., 2000). The primary aim of this dissertation was to investigate the interplay between chronic stress and EF in detail. A three-year longitudinal cohort, the StressCog cohort, was established for this purpose. In order to understand the longitudinal interplay between chronic stress and EF, methodological foundations and cross-sectional matters had to be investigated first. As a result, this dissertation encompasses the following three studies: With classical laboratory designs, the estimation of generalizable and robust effects on the relationship between chronic stress and EF is impaired. Therefore, the StressCog study was set up to make use of internet-based data assessment within domestic environments. Study 1 addressed the feasibility of internet-based response time data, including the common concern that internet-based response time data collected in domestic environments is subject to increased data variability (Chetverikov & Upravitelev, 2016; Reips, 2002). To this end, performance measures collected in the laboratory were compared with measures collected in domestic environments. We found that a setting-related difference in the variability of conventional performance measures (i.e., response times and error rates), as well as diffusion model-based measures is only of small size. An overall increase of variance of approximately 5% was visible in domestic environments. However, as internet-based assessments allow for the recruitment of larger sample sizes (Reips, 2002) the loss of static power can be easily compensated. Therefore, the findings of Study 1 support the use of internet-based cognitive data collection in domestic environments. This formed a valuable basis regarding the collection and interpretation of the StressCog data used in Study 2 and Study 3. In order to get a broad picture of chronic stress the StressCog study aimed for multimethod assessment. The subjective (i.e., perceived) extent of chronic stress and conceptually related constructs were assessed by multiple self-reported measures. The objective (i.e., physiological) extent of chronic stress was assessed via hair cortisol concentration, which has been established as a widely accepted biological marker of chronic stress (E. Russell et al., 2012; Stalder & Kirschbaum, 2012). Surprisingly, however, multiple studies have shown that hair cortisol concentration is, at best, only weakly correlated with subjective chronic stress (Stalder et al., 2017; Staufenbiel et al., 2013; Weckesser et al., 2019). This lack of psychoendocrine covariance was addressed in Study 2 by investigating the construct validity of commonly used chronic stress instruments. A multidimensional item response theory approach was applied in order to display the overlap between items of commonly used measures of chronic stress, depressiveness, and neuroticism. A common latent scale covered the major amount of variance (40% to 48%). It appeared that the overlap of content is mainly based on fatigue, which is a core symptom of depressiveness. Similar to previously reported findings, the common latent scale displayed only a weak association with hair cortisol concentration. It can therefore be argued that items of self-reported chronic stress do not reflect the physiological (i.e., endocrine) aspect of chronic stress to a satisfactory extent. Thus, the results of Study 2 were a valuable basis for the interpretation of chronic stress data in Study 3. In Study 3, we investigated the cross-sectional association between chronic stress and EF. The study made use of data from the baseline assessment of the StressCog cohort (N = 514). Using structural equation modelling, we found no evidence for a meaningful association between chronic stress (i.e., self-reported measures and hair cortisol concentration) and a common latent EF factor. The results found in Study 3 were further supported by unpublished longitudinal StressCog data and analyses making use of diffusion model performance measures. Considering the mainstream of existing findings, which suggests chronic stress to be negatively associated with EF (e.g., Deligkaris et al., 2014; Sandi, 2013), an absence of an association between chronic stress and EF seems surprising. However, other existing findings support this perspective (Castaneda et al., 2011a; McLennan et al., 2016). Beyond this, the results of Study 1 and 2 help to explain why a lack of an association between chronic stress and EF is quite plausible. As within traditional, laboratory-based settings a recruitment of larger samples sizes is difficult and costly, most existing studies lack large, representative samples. In consequence, many findings are based on narrow sample characteristics. Supported by the findings of Study 1, the StressCog study made use of internet-based data collection, which led to the establishment of one the largest, population-based cohorts in the field. Thus, the results presented in this dissertation can be seen as much more robust and representative than many other studies that suggest opposing results. The findings of Study 2 allow for the assumption that many studies in the field make use of questionable self-report instruments and that subjective (i.e., self-reported) measures of chronic stress are only weakly related to objective (i.e., HCC) measures. In consequence, results always depend on the operationalization of the chronic stress measures being used. Caution is advised when comparing opposing results of different measures. With regard to our daily life demands, it may appear quite promising that no association between chronic stress and EF was found in this dissertation. However, these results should not be misunderstood. It has been demonstrated countless times that chronic stress can severely affect the human organism, causing various negative effects that go far beyond a possible impairment of cognitive abilities. Knowing that chronic stress can impair EF under certain circumstances leads to the central question of what conditions make stress toxic. In order to answer this question further systematic research is needed, in which representative samples and experimental study designs will be of crucial help. As long as these questions are not satisfactorily clarified, it seems best to deal with the challenges of chronic stress in a conscious and responsible manner.