Recent advances in sensors and wireless RF technologies and their convergence with the Internet offer vast opportunities for development and application of sensor systems for agriculture. The objective was to create regional and on-farm sensor networks that provide remote, real-time monitoring and/or control of important farming operations that add value through improved efficiency and efficacy of targeted management practices. This paper describes hardware and software components of technologies developed for regional and on-farm sensor networks and their implementation in agricultural applications in Washington State. The regional sensor network consists of a data logger equipped with a 900 MHz frequency hopping spread spectrum (FHSS) radio configured into master-repeater-slave network for broad geographic coverage. A single master is configured with multiple repeaters to provide line-of-sight telemetry backbone networks with multiple master-repeater configurations integrated via the Internet into a single network. Software includes firmware, client software to manage and operate a network on a personal computer, and Internet software to supply data and information products to users. The on-farm sensor network consists of new 900 MHz FHSS radios with varying telemetry and data logging capabilities for integrated short and long-distance network configurations. Firmware supports various telemetry topologies and a range of analog, digital, pulse counter, switching, and serial devices. A single BASE radio is responsible for radio synchronization and data collection from REMOTE stations in a network, temporarily stores that data, and then broadcasts data to ROAMER units connected to computers and/or directly to the Internet. Software operating on a computer connected to a ROAMER collects, manages and display data, and has functionality for transmitting control instructions to REMOTES via the BASE. Four agricultural network applications are described including a regional and site-specific weather network, a regional vehicle tracking network, and on-farm frost protection and irrigation monitoring and control networks.