This paper describes how Tralics converts a sequence characters into a sequence of tokens, into a math list, and finally into a MathML formula. Tokenisation rules are the same as in TeX, the meaning of these tokens is the same as in LaTeX, and can be given in packages. Math formulas are handled in the same spirit as TeX, but construction of the MathML result is not obvious, due to particularities of both TeX and MathML.