1. Undue Influence

Undue influence is the most common ground for will and trust contests. It applies when someone in a position of trust or control over the testator (the person making the will or trust) used that position to override the testator's free will and cause the document to reflect the influencer's wishes rather than the testator's.

What courts look for:

• The alleged influencer's vulnerability — was the testator elderly, ill, isolated, dependent, or cognitively impaired?
• The alleged influencer's apparent authority — did they have a confidential relationship, caregiving role, or fiduciary position?
• The alleged influencer's actions — did they arrange the appointment with the attorney, transport the testator, isolate them from other family members, or participate in preparing the document?
• The unfairness of the result — does the challenged document reflect a significant change from prior estate plans that particularly benefits the alleged influencer?

Late-life amendments — particularly trust amendments made in the last months of the testator's life — receive heightened scrutiny under California law. Amendments that isolate other family members, dramatically shift assets to caregivers, or contradict long-stated intentions are red flags.

Legal framework: Welfare & Institutions Code §15610.70 (defining undue influence for elder law purposes); Probate Code §§21380-21392 (presumptions of undue influence for certain transferees).

2. Lack of Testamentary Capacity

To make a valid will or trust, the testator must have testamentary capacity at the moment of execution. This is a specific legal standard — different from general mental competency, and different from the standard for other transactions.

To have capacity, the testator must understand:

• The nature of the act — that they are making a will or trust
• The nature and extent of their property
• Their relationships with those who would naturally be objects of their bounty (family members, close friends)
• How the will or trust distributes their property

Capacity can be temporarily present or absent. A person with progressive dementia might have capacity in the morning and lack it in the afternoon. A person on certain medications might have capacity when the medication has worn off and lack it when it's peak-effect. What matters is capacity at the moment of execution — which is often the central factual dispute in capacity cases.

Capacity challenges typically rely on medical records, expert testimony from geriatric psychiatrists or neurologists, testimony from witnesses who observed the testator around the time of execution, and evidence of specific cognitive impairments documented at the time.

Legal framework: Probate Code §§810-812 (mental capacity standards); Probate Code §6100.5 (testamentary capacity for wills).

3. Fraud in the Execution

Fraud grounds apply when the testator was deceived about the nature or contents of what they were signing, or was induced to sign by false representations.

Common fraud scenarios:

• Fraud in the execution: The testator was told they were signing one document but was actually signing something else
• Fraud in the inducement: The testator was told false facts that caused them to make provisions they otherwise wouldn't have made (for example, being told falsely that a family member had died, refused to visit, or committed some act)
• Forgery: The signature is not actually the testator's

Fraud claims typically require detailed factual investigation — examining who was present when the document was signed, whether the testator had opportunity to read what they signed, whether independent counsel was involved, and whether prior estate plans support or contradict what the challenged document says.

Legal framework: Common law fraud principles; Probate Code §21380 (fraud presumption for certain transferees).

4. Improper Execution

California has specific formalities for validly executing a will or trust. Failure to comply with those formalities can invalidate the document — even if it accurately reflects what the testator wanted.

Will execution requirements (Probate Code §6110):

• In writing
• Signed by the testator (or someone at the testator's direction in the testator's presence)
• Signed by two witnesses who observed the testator sign the document (or acknowledge the signature)
• Witnesses must sign in the testator's presence and know they are signing as witnesses

Trust execution requirements: Less formal than wills — a trust need only be in writing and signed by the settlor. However, revocable trusts often reference wills or pour-over provisions that require will formalities to work as intended.

Improper execution challenges typically focus on witness testimony (were witnesses actually present, did they know what they were witnessing), signature analysis (is the signature genuine), and document analysis (is the document complete, has it been altered).

Legal framework: Probate Code §6110 (will execution); Probate Code §§15200-15208 (trust creation and execution).