The beliefs of preservice elementary-school teachers regarding the use of basic calculators and "Illuminations" activities were investigated. The goals of the study were to describe preservice teachers' beliefs, identify the sources of those beliefs, and determine which interventions successfully modify them. Participants included 210 undergraduates majoring in elementary education or special education. Results indicate that many preservice teachers oppose the use of calculators during mathematics instruction. Teachers report that this belief is related to their own elementary-school experiences and to their own computational abilities. Other teachers believe that calculators and computers can be used as teaching tools but caution that they should not be over used. An introductory methods course positively affected the beliefs of preservice teachers. Researcher-designed calculator interventions did not significantly affect their beliefs. Preservice teachers who have use "Illuminations" activities have very favorable beliefs about them and plan to use them in their classes.