An expression meaning one cannot help doing something or cannot suppress an impulse; formed with the negative base + ずにはいられない (e.g., 'can't help but...').
彼の冗談は面白くて、笑わずにはいられない。
His jokes are so funny that I can't help laughing.
あの子犬を見ると、助けずにはいられない。
When I see that puppy, I can't help but help it.
その話を聞いて涙が止まらずにはいられなかった。
Hearing that story, I couldn't stop myself from crying.