between you and I
The case of a pronoun in a compound object, as after between.
Use between you and me. Between is a preposition, and the object of a preposition takes the objective case (me, him, her, us, them).
Between you and I is a grammatical error: it puts the subjective case after a preposition. It comes from hypercorrection, in which speakers wrongly treat I as the polite or formal form in every compound.
Each pronoun in a compound object takes the objective case, because the conjunction does not change the role the pronoun fills: me in between you and me is the object of between, just as me in a seat beside me is the object of beside.
Two tests confirm the case.
Drop the rest of the compound: with Sam and I fails because with I fails, and with Sam and me passes because with me passes.
Replace the compound with one plural pronoun: between you and me becomes between us, and us is in the objective case, so me is the form inside the compound.
The ruling covers every preposition and every pronoun in a compound object: with him and me, from her and Amy, about them and us. It also covers a compound object of a verb: The host seated Laura and me together; Let Rachel and me close up tonight.
Myself cannot replace me in a compound object. Myself is a reflexive or intensive pronoun, and it needs the antecedent I in the same clause: I painted the hallway myself. Between you and myself is nonstandard; use me.
See also I / me / myself; case in compound and coordinated pronouns; joint subjects and pronoun case; myself as polite subject; intensive pronouns / reflexive pronouns; among / between.
Examples
Use The neighbors left a casserole on the porch for Jordan and me. (Jordan and me is the compound object of the preposition for.)
Use The landlord divided the repair bill between Marcus and me. (Me is part of the compound object of between.)
Avoid Between you and I, the new schedule won’t last a month. (I is the error: the object of the preposition between takes the objective case. Write Between you and me, the new schedule won’t last a month.)
Avoid The manager asked Carlos and I to cover the weekend shift. (I is the error: Carlos and I is the compound object of asked, so the pronoun takes the objective case, as asked me shows. Write The manager asked Carlos and me to cover the weekend shift.)
Avoid Things have been tense between she and Kevin since the office move. (She is the error: the object of the preposition between takes the objective case. Write Things have been tense between her and Kevin since the office move.)
Avoid Thank you for driving my wife and myself to the airport. (Myself is the error: no I in the clause serves as its antecedent. Write Thank you for driving my wife and me to the airport.)