A Google search gives a few possibilities, and I'm not sure how these differ or which would be appropriate:
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Einleitung would be the most common, I think. Einführung (which can also mean insertion, depending on context) is not wrong, but usually refers to something broader, like an introductory course or similar. Your last two examples (i.e. Bekanntschaft and Vorstellung) refer to persons being introduced or getting to know one another.