Language Learners’ epistemological beliefs (LLEBs), as their conceptions about the nature of L2 knowledge and L2 knowing, are among the determinants of the route and the outcome of language learning; however, research into their dimensional and developmental nature is at the premium. This qualitative study was designed to (a) unravel the dimensions of LLEBs, and (b) delineate data-driven dimension-specific developmental patterns. Following “maximum variation” sampling, data obtained in 30 one-to-one semi-structured oral interviews were subjected to directed qualitative content analysis to detect utterances related to L2 knowledge and knowing conceptions. Seventeen themes each reflecting beliefs about one of epistemological beliefs’ core dimensions (i.e., knowledge certainty: N=4; simplicity: N=4; source: N=5; and justification: N=4) were extracted, and inter-coder agreement ensured. In the second phase, data obtained in three separate focus-group interviews from another 18-member sample selected via “critical case sampling” were analyzed to sketch differential dimension-related beliefs, if any, and sketch possible developmental paths. The results showed clear distinctions across the three sub-samples in terms of all the 17 LLEBs’ themes extracted in phase 1, roughly reflecting Baxter Magolda’s (1992) four-point epistemological development continuum from “absolute knowing” through “transitional knowing” and “independent knowing” to “contextual knowing.” The findings indicate the dimensionality and developmental nature of LLEBs, and the alignment of LLEBs with research on domain-general epistemology.