Excessive persuasion that overcomes a person’s free will and causes them to make a decision or execute a document (like a will, trust, deed, or gift) that reflects the influencer’s desires rather than their own true intent. It involves more than just ordinary persuasion or advice. Under California law, undue influence is a common ground for contesting the validity of wills, trusts, and other documents, especially when the person making the document was vulnerable (due to age, health, or isolation) and the influencer was in a position of trust or took actions to manipulate the outcome. If proven, the influenced document or transfer may be invalidated by the court. (See Cal. Prob. Code § 6104; Welf. & Inst. Code § 15610.70).