A Power BI developer integrates data from multiple sources by utilizing Power BI’s wide range of data connectors. They connect to databases, cloud services, APIs, and flat files, importing data into Power BI’s data model. Using Power Query, they clean, transform, and combine data from these disparate sources into a unified format. Power BI developers then creates relationships between different datasets, ensuring seamless data integration. This allows for comprehensive analysis and reporting, enabling stakeholders to view and compare data from various sources within a single Power BI dashboard.