Atrial fibrillation requires a trigger that initiates the arrhythmia and substrate that favors perpetuation.  Cardiac mapping is necessary to locate triggers and substrate so that an ablation strategy can be optimized.  The most commonly used cardiac mapping approach is isochronal or activation mapping, which aims to create a spatial model of electrical wavefront propagation.  Historically, activation mapping has been successful for mapping point source and single or double wave reentrant arrhythmias, while mapping multiple wavelets or driving sources that underlie most episodes of atrial fibrillation remains challenging.   In the multiple wavelet model of AF there is no particular area critical to sustain atrial fibrillation, and a “critical mass” of atrium is required to maintain AF.  Recent studies suggest endocardial and epicardial dissociation may play an important role.    Investigation of driving sources that sustain AF has focused on the presence of rotors.  Rotors in human AF have now been observed using multiple imaging modalities, however ablation strategies targeting rotors remain of unproven benefit.  In addition, substrate mapping of AF is now feasible.  Increasing degrees of atrial fibrosis on delayed enhancement magnetic resonance imaging (DE-MRI) has been shown to correlate with poor procedural outcomes for AF ablation, which suggests the increased burden of scar promotes more complex and extensive arrhythmia substrate. Atrial fibrosis is also identifiable using electrogram voltage tagging in an electro-anatomic mapping system.  Patient-specific ablation strategies targeting areas of fibrosis are currently under investigation.  Recent technological advances have facilitated greater understanding of the potential role for AF mapping and has allowed initiation of clinical studies to evaluate the effectiveness of mapping-based intervention.  Multi-modality mapping is likely to play an increasingly important role in AF ablation, but is currently limited by the inability to simultaneously record and interpret electrical signals from both atria and from both the epicardium and endocardium.