The goal of this systematic review was to investigate correlations between baseline functional connectivity (FC) and treatment response to repetitive transcranial magnetic stimulation (rTMS). FC is a term for neuronal networks within and between different brain regions. The strength of these networks varies between individuals and can be measured using different tools. The most used technique is functional magnetic resonance imaging (fMRI), which detects active brain cells or neurons through their increased need for oxygen from red blood cells. In addition, an electroencephalogram (EEG) can be performed. EEG measures brain activity using electrodes. This can be translated into connectivity between brain regions when the activity is measured at different locations on the scalp simultaneously. At last, single photon emission computed tomography (SPECT) and arterial spin labelling (ASL) can be conducted to measure regional cerebral blood flow (rCBF). This is higher when neurons are activated. The techniques use a tracer, which is a specific substance that can be followed in the body. SPECT uses a radioactive tracer to create an image of the brain, whereas ASL uses magnetically labelled water protons from arterial blood as tracer, measured with MRI. This makes ASL less invasive and thus less dangerous. For this systematic review it was important that the included studies measured FC at baseline, meaning before the start of the intervention. This way, it was possible to correlate baseline FC with response to rTMS. rTMS is a technique where magnetic pulses are applied to the scalp via electrodes. It stimulates the nerve cells of deeper brain regions. This procedure is used in patients with depression who do not respond to the traditional psychotherapy and medication. In the included studies, response to treatment was assessed using several depression rating scales. These scales all measure clinical severity of the current depressive episode. Treatment response was defined as a percentage of reduction in scores post-treatment compared to baseline. To find eligible studies, an extensive search strategy was implemented in Pubmed, Embase, Web of Science and Scopus. Articles were collected from multiple databases. The results of this systematic review were diverse. Baseline FC between different brain regions appeared to be predictive of treatment response. Two important regions are the subgenual anterior cingulate cortex (sgACC) and the dorsolateral prefrontal cortex (DLPFC). The sgACC is part of the limbic system, a bigger part of the brain that regulates our emotions. The prefrontal cortex is linked to positive emotions. This reflects some of the key aspects of patients suffering from depression: loss of interest and pleasure, and depressed mood. Even though rTMS has been proven to be effective in depression, still many patients do not respond significantly to treatment. Identifying predictors of response would optimize cost-effectiveness by predefining which patients are eligible. This would be a major step forward, since rTMS treatment also comes with a burden. At first, the treatment is expensive. It typically consists of 20-30 sessions and each session comes with a certain price. Accumulated, this results in a considerable amount of money. In addition, it requires a lot of time. These sessions take place daily for several weeks. The device is only available in few hospitals, resulting in a daily time-consuming commute. Besides, this transportation is often logistically challenging. Therefore, this systematic review is of importance for clinical practice.