Compact_Eddy is a handheld computer-based logging system developed for eddy covariance installations. It is flexible to support different types of sonic anemometers, it has storing capability on internal memory, and data processing capability. The software is written in the Visual Basic .NET platform, entirely based on standard Windows operating systems thus allowing easy installation and configuration for a wide range of handheld PCs. The software computes half hourly statistics and fluxes with a simplified procedure, stores binary data with efficient memory usage and can be configured to send periodically, to a remote control station, system status information and basic computations using a GSM modem. The use of a handheld computer resulted in an average real conditions power consumption of 2.9 W, very low if compared with other standard logging devices, allowing important savings especially when systems are powered with solar panels in remote areas. Compact_Eddy has been installed and tested in three locations, with very different environmental conditions ranging from eastern European mountain forests to African semi-desertic areas. The field results demonstrated that the system operated reliably, resulting to be a good low-cost alternative to laptop computers and dataloggers. © 2008 Elsevier B.V. All rights reserved.