A discussion of some student conceptions of the solid-liquid and liquid-vapor phase transitions is presented. Data from open-ended, short-answer questions were collected from first-semester general chemistry students and then discussed in the context of previous studies. The responses gave insight into the various student conceptions about these phase changes. Student misunderstandings were most often related to (i) contextual difficulties with the terms "freezing" and "boiling" associated with their lack of experience with different substances, (ii) misinterpretation of physical and chemical phenomena, either from everyday experience or classroom demonstrations, and (iii) the inability to understand energy transfer processes. Specific implications for the teaching of topics related to "freezing" and "boiling" are also addressed.