This dissertation addressed one of the most pervasive aspects of human cognition: internally oriented attention during mind wandering. During a large part of our day-to-day lives, our attention is not focused towards the external word around us, but inwards, towards internal thoughts and feelings that are unrelated to the here and now. My aim was to better understand what happens in our bodies and brains as we detach ourselves from the external physical environment when mind wandering. In Chapter 2, I present findings from various studies investigating how individuals mind wander under a variety of contexts, ranging from performing monotonous laboratory tasks to interactive classroom settings. I demonstrate that bodily and brain signals change during episodes of mind wandering and that these signals can be potentially used to catch a mind wandering episode and bring attention back to the present task. In Chapter 3, I used mouse-tracking as a method to investigate how motor movements change whenever individuals are mind wandering during an attention demanding online task lasting approximately 20 minutes. During the task, participants had to memorize a continuous stream of letters while at the same time performing mathematical operations on the screen. After each series, participants were asked to recall the stream of letters in the correct order. The entire task was performed with a computer mouse. What I found was that whenever participants were mind wandering, they took longer to initiate a response with the mouse. They also flipped the mouse back and forth more during a response. These findings demonstrate that mind wandering is reflected in slower and less direct movements during performance of an attention-demanding online task. In Chapter 4, I again investigate how motor movements change whenever individuals are mind wandering, but this time during a monotonous tasks. During the task, participants had to track the path of a ball bouncing back and forth from each corner of the screen. That is, they had to keep the mouse cursor within the ball for approximately one hour. Whenever the ball became red, participants had to click on it as quickly as possible. Whenever participants were mind wandering, they made more mistakes in tracking the ball such that the distance between participants’ mouse cursors and the ball became greater. The deeper their minds were wandering, the more mistakes participants made. In Chapter s, I was interested in whether a tendency to mind wander in daily life affected how much individuals actually mind wandered during performance of a monotonous tracking task. It is generally assumed that individuals who report mind wandering more in daily life should also mind wander more in most situations. However, I found no such correlation. Participants who reported mind wandering more in daily life did not report more episodes of mind wandering during performance of a monotonous tracking task. Interestingly, however, these individuals reported having less varied thought content during the task, suggesting that they may have been more absorbed in a single train of thought. In Chapter 6, I investigated what brain signals are activated whenever individuals are mind wandering during a monotonous tracking task. I found that individuals processed rare instances of changing stimuli more weakly whenever they were mind wandering, as indicated by a lower P3 component – a brain signal associated with conscious visual processing. Moreover, I found that low frequency brain waves ( delta, theta, alpha), typically stronger during sleep, were also more active during mind wandering. This is consistent with findings from previous studies measuring brain signals during performance of different types of tasks. Finally, I found for the first time, that individuals who report having a greater tendency to mind wander in daily life also seemed to have generally more active low frequency brain waves. The applications of these findings are manifold. Imagine having an instrument that is able to monitor your driving behavior and determine from your steering movements, whether your mind has wandered off and alert you to pay attention towards the road. Or imagine an app that monitors your mouse movements or scrolls on a screen as you study materials online for an exam and can determine from these movements whether or not you are paying attention to the current task. With the rise of online education, being able to gain insight from students’ mouse movements, keystrokes, or scrolling behavior can enable educators to design courses in a manner that optimally captures attention and can be tailored to individual needs. In a different scenario, the findings of this dissertation also have relevant applications in the field of motor rehabilitation, where brain signals could be measured to determine an individual’s level of attention and used to guide a patient’s exercise regime accordingly. As discussed in this dissertation, the adverse effects of mind wandering depend largely on the context in which an individual mind wanders. There are situations in which it might be productive to actually stimulate an individual to mind wander, as associations reached through mind wandering could bring about creative solutions to problems. For instance, after presenting an individual with a complex problem, presenting them with a something akin to the monotonous visuomotor tracking task used in this dissertation might serve to stimulate an individual to mind wander and formulate more creative solutions to a problem. How then can we know whether our thoughts are “grounded” in the present physical environment or elsewhere “in flight?” The findings presented in this dissertation demonstrate that the our bodies are largely intertwined with our minds, and consequently, can give us cues about the whereabouts of our thoughts. When we are mind wandering, fine motor movement becomes slower, less direct, more complex, and more erratic. The deeper we mind wander, the more erratic our fine motor movements, indicating a greater disengagement with the present reality. Our brain signals process stimuli from the external environment more weakly and are more similar to brain waves active during sleep. These cues allow us to take a glimpse into individuals’ minds and make an informed guess as to whether they are “grounded,” focused on the present moment, or wandering “in flight.”