We classify all possible new scalar particles that can have renormalizable
linear couplings to Standard Model fields and therefore be singly produced at
colliders. We show that this classification exhausts the list of heavy scalar
particles that contribute at the tree level to the Standard Model effective
Lagrangian to dimension six. We compute this effective Lagrangian for a general
scenario with an arbitrary number of new scalar particles and obtain
flavor-preserving constraints on their couplings and masses. This completes the
tree-level matching of the coefficients of dimension five and six operators in
the effective Lagrangian to arbitrary extensions of the Standard Model.
