B1 Preliminary, widely known by its former name PET (Preliminary English Test), sits in the middle of the Cambridge English Qualifications suite. It's designed for learners who can understand the main points of clear, standard input on familiar matters, deal with most situations likely to arise while travelling, and write simple connected text on topics that are familiar or of personal interest.
The exam has three papers: Reading and Writing (90 minutes combined), Listening (around 35 minutes), and Speaking (10–12 minutes, taken with another candidate). Each paper contributes to a single Cambridge Scale Score, reported on a scale from roughly 120 to 170. The Cambridge Scale Score is designed to be comparable across exam sessions and across different Cambridge qualifications, which is part of why it maps so cleanly onto the CEFR (Common European Framework of Reference for Languages).
The CEFR is the international standard used to describe language ability, from A1 (beginner) through C2 (proficient). B1 Preliminary is built around the B1 level, but because scoring is reported on a continuous scale rather than a simple pass/fail, a strong result can actually certify a candidate at B2 — one level above the exam's own name — while a weaker result is still recognized at A2.
A B1 or B2 result on B1 Preliminary is widely accepted by schools and employers as proof of solid, functional English. Many learners use a strong result here as the springboard to B2 First (FCE), which is itself often required for university entry or professional roles that need confident everyday English.