As research has improved regarding Spanish in the US, its research regarding the lexicon and the lexical assessments of students of Spanish as a second language (L2) and as a heritage language (HL), also has improved specially during the last three decades (Chávez, 2017 forthcoming). In this descriptive work, we present several research results for the Spanish lexicon, as a L2 and as HL, for lexical exams and for teaching lexical items or lexicon. The overall results show that the HL students have higher lexical levels than HL students due to several variables including gender, socioeconomic status, reading and Spanish use at home among others. However, according to several researchers, they still have several limitations and variations. Finally, we present a tentative guideline to improve the lexical assessments in Spanish as a L2 and as a HL based on previous research.