This chapter reports results on spontaneous brain activity during wakeful rest. It focuses on findings obtained with electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), either acquired separately or simultaneously. The chapter discusses two approaches to analyze resting state activity with fMRI, namely reverse subtraction (activity correlated with task deactivation) and independent component analysis (ICA)-based region analysis. A third way to explore resting state blood oxygen level-dependent (BOLD) activity is to add information obtained with independent recording modalities, in particular EEG. When EEG and fMRI are recorded simultaneously, fMRI activity patterns associated with EEG-defined brain states can be analyzed. Relaxed wakefulness in the EEG is characterized by alpha and beta band oscillations. A thorough analysis of EEG and fMRI patterns during wakeful rest yields a complex relationship where certain EEG patterns can be associated with different BOLD maps and vice versa.