The Irrigation Monitor tool is a Web-based application available at MyCWP, the partition for registered users of The Crop-Weather Program for South Texas, an online decision support system developed to help crop managers make more informed crop management decisions. The Irrigation Monitor tool allows irrigators to estimate how an irrigated crop uses the last applied irrigation water and any additional rainfall amount, thus providing useful information for irrigation scheduling and/or the adjustment of irrigation systems. This tool applies only to cotton and is usable only when irrigation records have been entered in advance using the My Irrigation online tool available at My Field Observations, a sub partition within MyCWP. Irrigation records are archived in a user-controlled database and each record consists of the date of an irrigation event, the amount of water applied, a discrete qualitative description of the stress condition of the crop (selected from a dropdown menu of options), and an average value of plant height at the time of irrigation. This information is then used to generate the needed inputs to run the Irrigation Monitor program. Upon selecting a particular irrigated field (listed in the user's Field Profiles list) and launching the Irrigation Monitor tool, the program automatically retrieves location, weather, soil, cultivar, and other data needed to simulate the progression of crop growth and canopy development, crop water use, soil moisture storage throughout the soil profile. The most important output generated by Irrigation Monitor is the amount of water (irrigation and rainfall) left available to the crop since the last irrigation event expressed as percentage. Irrigation managers can use the Irrigation Monitor to schedule the application of the next irrigation.