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Background: Eczema is a chronic, itchy skin condition with onset typically in early childhood. Clinical trials compare health-related outcomes between two or more groups receiving different interventions. The Harmonising Outcome Measures in Eczema (HOME) initiative is an international collaboration working together to develop a core outcome set of outcome measures to be included in all eczema clinical trials to improve the comparability of outcome measures across trials. Aims & objectives: This thesis aims to inform two of the outcome domains recommended for measurement in eczema clinical trials by the HOME initiative group: long-term control of eczema and patient-reported symptoms. For the long-term control of eczema domain, the key objectives were to understand the concept of long-term control of eczema from key stakeholders’ perspectives and to develop an instrument to measure eczema control. For the patient-reported symptoms domain the key objectives were to explore the measurement model of the Patient-Oriented Eczema Measure (POEM) and inform interpretability of the scores of the POEM. Methods: To understand the concept of long-term control of eczema from key stakeholders’ perspectives, qualitative methods using online focus groups with people with eczema and caregivers of children with eczema across six countries, and an online survey of the HOME membership was conducted. To develop an instrument to measure eczema control, development of a conceptual framework, focus groups, expert panel design and feedback, cognitive interviews, and piloting of items was conducted. The measurement model of the POEM was explored using thought experiments and theoretical discourse. Anchor-based and distribution-based statistical approaches to examining the minimally important change score and the smallest detectable change were used to assess the interpretability of the POEM scores. Results: With regards to progressing the long-term control of eczema domain of the HOME initiative; ‘eczema control’ is suggested to be a multi-faceted experience. A patient-reported outcome measure of eczema control called Recap of atopic eczema (RECAP) has been developed and initial testing shows that it is appropriate for use in eczema clinical trials and routine care. With regards to progressing the patient-reported symptoms domain of the HOME initiative; mental experimentation suggests POEM was developed using approaches consistent with a formative measurement model. Interpretation of POEM scores has been improved by understanding that a change in score that is two points or under is consistent with potential measurement error, and that changes in scores should be three points or more before the change is deemed to be clinically important. From the data available, there was no evidence that POEM scores require different interpretation according to disease severity, age, sex and ethnicity. Conclusions: RECAP and POEM are both patient-reported outcome measures that are fit for purpose for measuring long-term control of eczema and patient-reported symptoms (respectively) in eczema clinical trials. This body of work has contributed towards informing evidence-based consensus decisions by the HOME initiative.