Aims: Percutaneous left atrial appendage (LAA) occlusion has now become a suitable alternative to oral anticoagulation for stroke prevention in selected patients with atrial fibrillation (AF). However, LAA closure can be technically challenging and results suboptimal, in part due to variable left atrial anatomy.We aimed to characterize LAA morphology and identify potential anatomical pitfalls during LAA closure or LAA thrombus detection during transoesophageal echocardiography (TOE). Methods and Results: 103 patients with AF underwent cardiac magnetic resonance angiography to assess pulmonary venous anatomy. Adequate imaging quality was present in 76 in whom LAA morphology was assessed. The majority of LAAs (71%) were anterolaterally directed and 82% were 'claw'-shaped. However, there was significant variation in anatomy and course in the remainder: 11% were anteverted, 9% laterally directed and 9% retroverted. The shape was cone-like in 8%, fan-like in 5% and s-configured in 5% and there was significant variation in the curvature of the LAA body. While 66% had a single lobe, 30% were bilobed and 4% trilobed; 90% also had additional lobules. Conclusion: Our results demonstrate the significant variability of LAA geometry in AF patients. This may have implications for future device design for percutaneous LAA occlusion. The variable anatomy may affect LAA thrombus detection with TOE emphasizing the importance of multiple views to ensure complete assessment.