  In this paper, binary extremal singly even self-dual codes of length 40 and
extremal odd unimodular lattices in dimension 40 are studied. We give a
classification of extremal singly even self-dual codes of length 40. We also
give a classification of extremal odd unimodular lattices in dimension 40 with
shadows having 80 vectors of norm 2 through their relationships with extremal
doubly even self-dual codes of length 40.
