This study investigates the impact of head motion on functional connectivity MRI (fcMRI) estimates in a large sample of healthy young adults. Head motion, which varies significantly among individuals, was found to have systematic effects on fcMRI measures, particularly in large-scale networks such as the default and frontoparietal control networks. However, it also increased local functional coupling, such as between left and right motor regions. The study highlights the importance of considering head motion when interpreting fcMRI results, especially in group comparisons and studies exploring individual differences. Head motion was stable over time, suggesting that it may be a trait-like property that can confound analyses of genetic and heritability studies. Strategies to reduce head motion, such as better immobilization techniques and physiological signal regression, are discussed as potential solutions.This study investigates the impact of head motion on functional connectivity MRI (fcMRI) estimates in a large sample of healthy young adults. Head motion, which varies significantly among individuals, was found to have systematic effects on fcMRI measures, particularly in large-scale networks such as the default and frontoparietal control networks. However, it also increased local functional coupling, such as between left and right motor regions. The study highlights the importance of considering head motion when interpreting fcMRI results, especially in group comparisons and studies exploring individual differences. Head motion was stable over time, suggesting that it may be a trait-like property that can confound analyses of genetic and heritability studies. Strategies to reduce head motion, such as better immobilization techniques and physiological signal regression, are discussed as potential solutions.