Planets / Mercury
Personal
Mercury governs the rational mind, communication, and the way a person processes and exchanges information. It's the planet closest to the Sun and the fastest-moving in the sky (after the Moon), which shows clearly in its nature: mental quickness, curiosity, a need to name and understand what's perceived.
Mercury's sign in the birth chart describes a person's style of thinking and communicating: it can be direct and fast, reflective and cautious, scattered and curious, or meticulous and analytical, depending on the sign it occupies. It also shapes how someone learns, studies, and negotiates.
It's famous for its apparent retrogrades, three or four times a year, periods popularly associated with misunderstandings, delays, and technical glitches — in reality, they're good times to review, revisit, and close out pending communication, rather than to start new things.
The messenger of the gods, swift and clever, able to move between worlds: commerce, communication, and also trickery when words are used cunningly.
Gives mental clarity, ease with words, and the ability to learn and communicate complex ideas simply.
Can translate into mental scatter, trouble concentrating, or communication problems with close others.
During Mercury retrograde it's best to review, revisit, and close out rather than sign, launch, or buy new things: it's a good time to edit what's already underway.