Intracranial aneurysm (IA), a local outpouching of cerebral arteries, is present in 3 to 5% of the population. Once formed, an IA can remain stable, grow or rupture. Determining the evolution of an IA is almost impossible. Rupture of an IA leads to subarachnoid haemorrhage (SAH). SAH which mostly affects young people with a median age of onset between 50 and 60 years has heavy consequences in term of life, disabilities and socio-economic burden. Thus, even if the large majority of IAs will never rupture it is of high importance to determine which IA is at risk of rupture. IA (in)stability is dependent of its vascular wall composition. The biology of the IA wall is complex and not completely understood. Nowadays, in clinic, the risk of rupture of an IA can be estimated by using scores based on the characteristics of the IA itself such as location, size or presence of shape irregularities, and on the anamnesis of the patient including ethnicity, age, hypertension or smoking status. Such scores are not completely satisfying and more information concerning IA (in)stability are needed to safely determine if a patient should be observed or treated. In the present review, the effects of known risk factors for rupture, as well as the effects of biomechanical forces on the IA wall composition will be summarized. Moreover, recent advances in high resolution vessel wall magnetic resonance imaging which are promising tools to help in the discrimination between stable and unstable IA wall will be described. Common data elements recently defined to improve current state of knowledge in IA disease and disease management will be presented. Finally, recent findings in genetics will be introduced and future directions in the field of IA will be exposed.