Sensor networks are an exciting research area bringing together researchers with different backgrounds, from theory to practice. I will talk about data gathering in sensor networks, arguably a core task of many applications. I am going to look at data gathering from three different viewpoints, wireless theory, distributed computing, and networking protocols. In particular I will present results on worst-case capacity, data aggregation, and energy efficiency. Sensor networks continue to puzzle as many important ingredients are not well understood. In my talk I will point out a few open problems.