谢谢/謝謝 (xiè xiè) is the standard Mandarin expression for thank you. It is formed by repeating 谢 (xiè, to thank), with the second syllable commonly neutralised in tone in speech. Responses include 不客气 (bú kèqi, you're welcome), 没关系 (méi guānxi, no problem), or simply 不用 (bú yòng, no need). For more formal gratitude, 感谢 (gǎn xiè) or 非常感谢 (very grateful) are used. 谢谢 is among the very first expressions learners of Mandarin acquire.