Small molecule inhibitors of Stat3 and their derivatives are disclosed. Alsodescribed are methods to inhibit cellgrowth by use of Stat3 inhibitors, and the use of Stat3 inhibitors for theprevention and/or treatment of cancer. Further, inhibitorsof Stat3 that also do not inhibit Stat1 are described as well as theirderivatives. Methods of screening additional compounds forStat3 inhibition activity and/or non-inhibition of Stat1 activity are alsodescribed herein.