Common in blended-family planning: your surviving spouse is taken care of for life, but you (not they) control who ultimately inherits the principal. Assets qualify for the unlimited marital deduction if the trust is structured correctly.
Glossary · trusts
QTIP trust
Acronym: QTIP
In plain English
Qualified Terminable Interest Property trust — gives a surviving spouse income for life but preserves principal for your chosen heirs.