Technical Abstract: Risk of livestock losses to poisonous plants can be reduced on many ranges through prudent management based on application of existing knowledge. Poisonous plants can be categorized using both acceptability to livestock and a plant's toxic potential. Acceptability encompasses forage qualities such as taste and chemistry (i.e., nutrient and toxin concentrations) and postingestive feedback from an animal's daily and long-term (e.g., body condition) nutritional and toxicological state. Toxic potential reflects aspects of plant chemistry, including seasonal or other changes in concentration or functionality of the toxin(s), and type of toxicity (i.e., acute or chronic). Persistent livestock losses to poisonous plants may indicate that ranges are over-grazed or improperly managed. Aggressive management schemes that employ high stocking rates and grazing intensities may yield greater returns, but may also increase risk if poisonous plants are present. Plants may be ranked according to toxicity and acceptability. Six interrelated categories of plants are discussed: 1) always toxic and acceptable to livestock; 2) always toxic and not acceptable; 3) always toxic and acceptable at certain times; 4) toxic only at certain times and acceptable to livestock; 5) toxic at certain times and unacceptable; and 6) toxic at certain times and acceptable at certain times. Each category involves differing risk and uncertainty. Within this management matrix, strategies for dealing with specific poisonous plants can be customized depending on how much and when the plant is eaten by livestock, and when the plant is most toxic.