Background: Amyotrophic lateral sclerosis (ALS)/motor neuron disease (MND) is a systemic and fatal neurodegenerative condition for which there is currently no cure. Informal caregivers play a vital role in supporting the person with ALS, and it is essential to support their wellbeing. This multi-centre, mixed methods descriptive exploratory study describes the complexity of burden and self-defined difficulties as described by the caregivers themselves. Methods: Quantitative and qualitative data were collected during face-to-face interviews with informal caregivers from centres in the Netherlands, England, and Ireland. Standardised measures assessed burden, quality of life, and psychological distress; furthermore, an open-ended question was asked about difficult aspects of caregiving. Results: Most caregivers were female, spouse/partners, and lived with the person with ALS for whom they provided care. Significant differences between national cohorts were identified for burden, quality of life, and anxiety. Among the difficulties described were the practical issues associated with the caregiver role and emotional factors such as witnessing a patient’s health decline, relationship change, and their own distress. The mixed-methods approach allows for a more nuanced understanding of the burden and difficulties experienced. Conclusion: It is important to generate an evidence base to support the psychosocial wellbeing and brain health of informal caregivers.