An ArcGIS SDK developer works on the creation and maintenance of software applications using the ArcGIS Software Development Kit. They design, build, and test geographic information systems (GIS) applications, integrating geospatial data, mapping, geocoding, and geoprocessing. They also fix bugs, optimize performance, and ensure the application's compatibility with various devices and systems. Developers work closely with end-users to understand their needs and translate them into functional software solutions. They often collaborate with other developers, data scientists, and GIS analysts, using their expertise in programming languages like Python, .NET, Java, or JavaScript.