There are strong pragmatic and moral reasons for receiving societies to address access to healthcare for migrants. Receiving societies have a pragmatic interest in sustaining migrants' health to facilitate integration; they also have a moral obligation to ensure migrants' access to healthcare according to international human rights principles. The intention of this thesis is to increase the understanding of migrants' access to healthcare by exploring two study aims: 1) Are there differences in migrants' access to healthcare compared to that of non-migrants? (substudy I and II); and 2) Why are there possible differences in migrants' access to healthcare compared to that of non-migrants? (substudy III and IV). The thesis builds on different methodological approaches using both register-based retrospective cohort design, cross-sectional design and survey methods. Two different measures of access were used to explore differences: 1) cancer stage at diagnosis as a clinical outcome and 2) emergency room (ER) contacts as a utilisation measure. Both informal and formal barriers to access were studied to explore why possible differences existed including: 1) motivation for using ER; and 2) asylum seekers' healthcare entitlements. Different definitions of migration and ethnicity were investigated including: country of birth and residence status. Substudy I showed a tendency towards more advanced stage at diagnosis or unknown stage among most subgroups of migrant women with a history of cancer compared to non-migrant women. Sub-study II found that some migrants (those born in Somalia, Turkey and Ex-Yugoslavia) use ER services more frequently than do non-migrants whereas others have the same or lower utilisation levels. As a consequence, substudy III was undertaken, which documented that more migrant within all subgroups had considered contacting a primary caregiver before visiting the ER compared to non-migrants, but that migrants experienced communication problems herein. Additionally, more migrants had irrelevant ER visits as evaluated by caregivers. Substudy IV addressed formal and informal barriers to access and screening. According to the law asylum seekers are entitled to emergency care only in 10 out of 24 countries. Medical screening was carried out in all but one of the 24 EU countries; however, the content and extent of screening programmes vary. The thesis aimed to explore if there are differences in migrants' access to healthcare compared to that of non-migrants. Differences in utilisation and clinical outcome were identified between migrants and non-migrants. Reasons why disparities exist were also identified in relation to communication with primary care and on policy level. The thesis shows that various perspectives and scientific problems are important to get a full understanding of the process of access to healthcare for different migrant groups. Moreover, various complementary methodological approaches are needed when studying problems of migrants' access to healthcare.