What it usually means
A twin is someone who shares your beginning. Twins look alike, often think alike, and yet are separate people. Dreams about a twin usually concern this strange closeness: another version of yourself, or two sides of one person.
Duality is the first theme. Dreaming that you have a twin, especially one you do not have in waking life, often reflects two sides of your own character: the careful one and the reckless one, the public self and the private one. The twin can show the part you live less.
Comparison is the second. Twins are always compared. A twin dream can reflect a sense of being measured against someone — a sibling, a colleague, a former self — and found better or worse.
Closeness is the third. Twin dreams sometimes concern a person you feel deeply connected to, a friend or partner who seems to understand you without words.
Inner conflict is another meaning. Twins who fight, compete or work against each other in a dream often reflect a decision in which two parts of you want different things.
If you are a twin yourself, the dream may simply be about your sibling, your shared history and the space between you now.
Rivalry is a related theme. Twins compete for attention, praise and love from the same people. A twin dream can bring up old rivalries with brothers and sisters, or present ones at work, where someone seems to be living the life you were meant to have.
Worth saying plainly: dreams of twin babies can arrive during pregnancy or when someone is thinking about children. They can also reflect two projects or plans growing at the same time.
What changes the meaning
Discovering you have a twin. Meeting an unknown side of yourself.
An evil twin. A part of yourself you reject or fear.
A twin who is better than you. Comparison; feeling you fall short.
Twins fighting. Inner conflict; two desires pulling apart.
Twins working together. Integration; two sides cooperating.
Losing a twin. Losing a part of yourself or a deep bond.
Being mistaken for your twin. Confusion about identity; others not seeing who you are.
Twin babies. Double responsibility; two new beginnings.
Identical twins. Repetition; something happening twice.
Twins who look different. Two very different possibilities from one root.
Your real twin in the dream. Your relationship with them now.
A twin who is dead. A road not taken; a self you no longer are.
When it keeps coming back
Recurring twin dreams often appear during choices between two paths, when both seem possible and both seem to belong to you.
They also come in periods of change in identity — a new job, a move, a recovery — when a former self and a new self exist side by side for a while.
Some people dream of a twin after a close friendship or partnership has ended. The twin can stand for the person who once mirrored them, and for the part of themselves that left with that person.
If you keep dreaming of a twin, notice what the twin does that you do not. That is often the part of you asking for room.
In Jungian terms
In Greek myth, the twins Castor and Pollux were born together, but only Pollux was immortal. When Castor was killed, Pollux begged Zeus to let him share his brother's fate. Zeus allowed them to divide immortality between them, and the twins spend their days alternately among the gods and in the underworld.
Jungian readers see in the story the relation between the ordinary self that lives and dies and something larger that does not. The two cannot be fully separated, and each needs the other.
A twin dream may point to that partnership. Not choosing between two halves of yourself — but letting them share the same life.