Multitasking-based use of Information Technology, a term that we label MUIT, to accomplish work-related tasks has become a common behavior for employees in organizations. Despite this reality, most research to date has focused on studying either the use of one IT at a time or multi-tasking behaviors in experimental laboratory settings. As a result, this study aims to fill these gaps. Building upon cognitive load theory and multiple resource theory, this paper theorizes that MUIT positively influences cognitive load, which in turn, has a curvilinear (concave, in-verted U) relation with performance. In order to test our hypotheses, we employed the Experi-ence Sampling Method (ESM), a special form of diary study, to gather data on employees at multiple occasions for two weeks. The collected data are hierarchical (multiple observations within individuals), and thus, we employed multi-level regression to test the hypotheses. Results show, as hypothesized, a positive relation between MUIT and cognitive load, and an inverted U relation between cognitive load and performance. Therefore, this study demonstrates that in work settings although MUIT increases cognitive load, cognitive load is not always detrimental: some cognitive load has positive effects on performance until it reaches a tipping point where performance starts to suffer.