The Will statute which regulates Last Will and Testaments in Pennsylvania is chapter 25 of title 20, the probate, estates and fiduciaries code:
§ 2501. Who may make a will. Any person 18 or more years of age who is of sound mind may make a will. § 2502. Form and execution of a will. Every will shall be in writing and shall be signed by the testator at the end thereof, subject to the following rules and exceptions: (1) Words following signature.–The presence of any writing after the signature to a will, whether written before or after its execution, shall not invalidate that which precedes the signature. (2) Signature by mark.–If the testator is unable to sign his name for any reason, a will to which he makes his mark and to which his name is subscribed before or after he makes his mark shall be as valid as though he had signed his name thereto: Provided, That he makes his mark in the presence of two witnesses who sign their names to the will in his presence. (3) Signature by another.–If the testator is unable to sign his name or to make his mark for any reason, a will to which his name is subscribed in his presence and by his express direction shall be as valid as though he had signed his name thereto: Provided, That he declares the instrument to be his will in the presence of two witnesses who sign their names to it in his presence. § 2503. Nuncupative wills (Repealed). § 2504.1. Validity of execution. A will is validly executed if executed in compliance with section 2502 (relating to form and execution of a will), or in compliance with the law of the jurisdiction where the testator was domiciled at the time of the execution of the will or at the time of his death. § 2514. Rules of interpretation. In the absence of a contrary intent appearing therein, wills shall be construed as to real and personal estate in accordance with the following rules: (1) Wills construed as if executed immediately before death.–(Repealed). (1.1) Construction that will passes all property.–A will shall be construed to apply to all property which the testator owned at his death, including property acquired after the execution of his will. (2) After-acquired property.–(Repealed). (3) Devises of real estate.–All devises of real estate shall pass the whole estate of the testator in the premises devised, although there be no words of inheritance or of perpetuity. § 2701. Contracts concerning succession. (a) Establishment of contract.–A contract to die intestate or to make or not to revoke a will or testamentary provision or an obligation dischargeable only at or after death can be established in support of a claim against the estate of a decedent only by: (1) provisions of a will of the decedent stating material provisions of the contract; (2) an express reference in a will of the decedent to a contract and extrinsic evidence proving the terms of the contract; or (3) a writing signed by the decedent evidencing the contract. (b) Joint will or mutual wills.–The execution of a joint will or mutual wills does not create a presumption of a contract not to revoke the will or wills.