This thesis investigated whether inflammation is implicated in breast cancer aetiology and survival. For this purpose, circulating markers of inflammation and inflammatory clinical disorders were studied in relation to the risk, severity, and survival of breast cancer in a large Swedish cohort, the Apolipoprotein MORtality RISk Study (AMORIS), which includes >800,000 participants in Greater Stockholm area. Common inflammatory markers: serum C-reactive protein (CRP), albumin, haptoglobin and white blood cells (WBC) were examined in relation to breast cancer risk and survival using Cox proportional hazard regression models. Proportional odds models were employed to assess these markers with regards to breast cancer severity. Systemic inflammation was shown to be weakly associated with breast cancer risk and survival. Allergy, which has been increasingly linked to cancer in part through inflammation, was also evaluated using serum allergen-specific IgE against inhalant allergens. Overall, serum specific IgE was inversely associated with the risk of cancer particularly in women. A similar but weaker trend was seen for breast cancer. Serum lactate dehydrogenase (LDH), a marker of inflammation and metabolic alterations in cancer, was studied in relation to cancer survival. Among breast cancer patients, women with higher serum LDH were associated with worse overall survival, suggesting its relevance in breast cancer growth and progression. Associations between components of metabolic syndrome, which has often been linked to inflammation, and breast cancer survival were evaluated using prediagnostic serum glucose, triglycerides, and total cholesterol. In a competing risk analysis using latent class proportional hazard models, this association differed by patients characteristics, indicating a complex link where competing outcomes are involved. In summary, findings derived from this thesis contribute to a further understanding of the role of inflammation in breast cancer, and may provide directions towards future mechanistic and clinical research.