This study investigated the vocabulary learning strategies used by Thai high school students. The aim was to identify the frequency of different techniques used by high school learners studying in various programs. The main objective of this study was to compare the use of vocabulary learning strategies between multiple programs of study and examine the relationship between these different strategies. A total of 491 high school students from multiple academic disciplines participated in this study. A 47-item questionnaire of vocabulary learning strategies was given to the participants. In addition, qualitative data were collected via semi-structured interviews with 21 students to gain further information on their vocabulary learning strategy use. The interview recordings were immediately transcribed verbatim and translated from Thai into English by two experts. The results indicated that the most frequently used strategies were determination strategies, whereas memory strategies were used the least. The findings also showed that the learning context influenced the participants' use of vocabulary learning strategies. The qualitative results further revealed the variety of vocabulary learning strategies and the degrees of strategy use. In conclusion, this study highlighted that vocabulary learning strategies are interrelated, and the strategies adopted by learners can depend on vocabulary learning conditions.