## Introduction

Relationship by affinity describes how the law views your connection to your spouse’s blood relatives. In plain terms, it covers “in-law” and many step relationships created through a valid marriage. While it’s not a blood tie, it still matters in several areas of US law, including public employment rules, jury selection, marriage restrictions, and some family law issues.

This guide explains what counts as affinity, how degrees of relationship work, when affinity begins and ends, and where it affects real decisions. You’ll also find quick examples and a handy reference table for common situations.

## What You’ll Learn

- What relationship by affinity means in US law
- How degrees of affinity are commonly described, with everyday examples
- When affinity starts (and when it ends after divorce or death)
- How affinity differs from consanguinity (blood relation)
- Where affinity matters most: estates, custody and guardianship disputes, marriage restrictions, juror qualification, and nepotism rules
- Practical steps to apply these rules and how to check your state’s statutes

## Core Concepts

### What “relationship by affinity” means and common degrees

- Definition: Affinity is the legal relationship between a spouse and the blood relatives of the other spouse. It’s created by marriage, not by blood.
- Common examples of affinity:
  - Parent-in-law, child-in-law, stepparent, stepchild
  - Brother-in-law, sister-in-law
  - Grandparent-in-law, grandchild-in-law
- Degrees of affinity (general guide; state law may vary):
  - First degree: parents-in-law, children-in-law, stepparents, stepchildren
  - Second degree: siblings-in-law, grandparents-in-law, grandchildren-in-law
  - Third degree: aunts/uncles-in-law, nieces/nephews-in-law
- Two directions of affinity are often recognized in statutes:
  1. Your relationship to your spouse’s blood relatives (for example, your spouse’s sister is your sister-in-law).
  2. Your relationship to the spouses of your blood relatives (for example, your brother’s wife is your sister-in-law).

Note: Some statutes define degrees differently or apply them to specific contexts only (such as government nepotism rules). Always check the wording in your state.

### When affinity starts and ends

- Start: Affinity begins when there is a valid marriage recognized by the state.
- Divorce or annulment: In many contexts, affinity ends when the marriage ends. However, certain laws treat affinity as continuing if the marriage produced a child (for example, some state nepotism statutes keep the relationship for conflict-of-interest purposes).
- Death: Some rules treat affinity as ending at a spouse’s death; others keep it for limited purposes. For example, a few marriage-prohibition statutes still bar marriage to certain in-laws after a spouse dies, while other states permit it. The answer is state-specific.
- Domestic partnerships and civil unions: Whether these create “affinity” depends on state law. Some policies extend conflict-of-interest rules to registered domestic partners and their families.

Tip: For any real-world decision, read the statute or policy that uses the term “affinity.” Definitions and degrees can change from one law to the next.

### Affinity vs. consanguinity (blood relationship)

- Consanguinity: A blood relationship, such as parent, child, sibling, aunt/uncle, niece/nephew, cousin.
- Affinity: A relationship by marriage, such as in-laws and many step relations.
- Why the difference matters:
  - Intestacy (no-will) inheritance laws are built around blood relationships and spouses. In-laws typically do not inherit by affinity alone.
  - Many marriage restrictions focus on blood relations, but a number of states also include certain in-law relationships.
  - Jury service and public employment rules often reference both consanguinity and affinity within specified degrees.

## Key Examples or Case Studies

Real-life example: in-laws

- John marries Jane. John’s relationship to Jane’s sister is by affinity (sister-in-law). They are not related by blood, but the marriage creates a legal relationship recognized in many statutes.

Case study: inheritance dispute (intestacy)

- Scenario: Jane dies without a will. Her husband John makes a claim to her estate. Jane’s sister and parents also claim a share.
- How affinity factors in: John’s right to inherit comes from his status as a surviving spouse, not because he is related by affinity to Jane’s family. Intestacy laws first consider the spouse and blood relatives of the deceased. In-laws (such as a parent-in-law or sibling-in-law) do not inherit from each other simply because of affinity.
- Practical takeaway: John may receive most or all of Jane’s estate depending on state law and whether Jane left descendants. Jane’s parents or siblings may receive a portion only if the state’s intestacy statute provides for them. The fact that John is related by affinity to Jane’s family does not give him rights in their estates, nor does it give them rights in his.

Case study: custody/guardianship after a parent’s death

- Hypothetical: After Jane’s death, her sister seeks custody of Jane’s child. John, the child’s father, objects.
- What courts consider: A surviving parent’s rights usually come first unless the parent is unfit or other significant circumstances apply. The aunt’s close bond with the child is relevant to best-interest factors, but John’s legal status as the biological parent generally carries more weight.
- Where affinity appears: John and the aunt are related by affinity, but this label does not weaken John’s parental rights. Courts focus on the child’s best interests and the legal rights of parents and guardians.

Brief example: public employment and conflicts of interest

- A city manager cannot hire or directly supervise their son-in-law under the city’s nepotism policy, which often references “affinity within the second degree.” When the employee marries, the new in-law relationship can trigger mandatory recusal or reassignment under policy.

## Practical Applications

Where relationship by affinity often matters in the US:

- Marriage restrictions:
  - Most states bar marriage between close blood relatives.
  - Some states also restrict marriage between certain in-laws (for example, stepparent and stepchild). Others allow marriage to some in-laws, especially after a spouse’s death. Always check your state’s family code before applying for a marriage license.

- Estates and probate:
  - Spouses inherit from each other under state intestacy statutes; in-laws typically do not inherit solely because of affinity.
  - Disputes after death may involve the spouse and the decedent’s blood relatives, but the spouse’s rights are based on marriage, not on affinity to the decedent’s family.
  - Practical step: If there’s no will, review your state’s intestacy statute. If there is a will, follow the will unless successfully contested.

- Custody and guardianship:
  - A surviving parent usually has priority for custody.
  - An in-law (such as an aunt or grandparent by marriage) may seek guardianship or visitation in some states, but the standard is best interests of the child and any statutory standing requirements.
  - Practical step: File the correct petition and gather evidence about the child’s stability, caregiving history, and safety.

- Jury qualification and challenges for cause:
  - Many states allow removal of a potential juror who is related by affinity within a specified degree to a party, attorney, or witness.
  - Practical step: During voir dire, ask about in-law relationships and map them to degrees under the state’s rule.

- Government and school employment (nepotism/recusal rules):
  - Public-sector policies often restrict hiring, supervising, or contracting with relatives by affinity within certain degrees.
  - Practical step: HR should maintain clear definitions in policy manuals and ask employees to disclose in-law relationships that could create conflicts.

- Domestic violence and protective orders:
  - Some states define “family or household member” to include certain in-laws or step relations, while others do not.
  - Practical step: Check the definitions section of the protective order statute.

How to apply these rules with confidence:

1. Confirm the marriage status
   - Is there a valid marriage? If not, traditional “affinity” may not apply.

2. Identify the relationship
   - List the people involved and determine if the connection is by blood or by marriage.

3. Determine the degree of relationship (if relevant)
   - Apply your state’s degree chart. Note that different laws may define degrees differently.

4. Read the exact statute or policy
   - Look for definitions and exceptions (for example, whether affinity continues after divorce if there are children).

5. Document
   - Keep marriage certificates, birth certificates, custody orders, and any HR disclosures in one place.

## Summary Checklist

- Know the definition: affinity is a relationship created by marriage, not by blood.
- Recognize common in-law and step relationships that count as affinity.
- Map the degree only when a statute or policy requires it.
- Remember: spouses inherit from each other; in-laws typically do not inherit by affinity alone.
- In custody matters, parental rights usually come first unless a statute or court finding says otherwise.
- For juries and public employment, check degree-based rules and definitions in your state.
- Confirm whether affinity ends at divorce or death under the specific statute you’re using.

## Quick Reference

| Context                | How Affinity Typically Applies                            | What To Check First                          |
| ---------------------- | --------------------------------------------------------- | -------------------------------------------- |
| Marriage restrictions  | Some states restrict marriage to certain in-laws          | State family code definitions and exceptions |
| Intestacy (no will)    | Spouse inherits by statute; in-laws rarely inherit        | State intestacy statute and surviving family |
| Custody/guardianship   | In-laws may petition; best interests control              | Standing to file and best-interest factors   |
| Jury service           | Jurors related by affinity within X degrees may be struck | State juror qualification rules              |
| Public employment (HR) | Nepotism policies often include in-laws within degrees    | Policy manual and state/local statutes       |

Related terms to review: Degree of Kinship, Curtesy, Lineal Descendants, Executor or Executrix, Lucid Interval

Note: Affinity rules vary by state and by legal context. Always confirm the definition and degree scheme in the statute or policy you’re applying.

Relationship by Affinity in US Law: Meaning, Degrees, and Common Uses