A co-respondent is one of two or more people named by the plaintiff in a civil lawsuit. Although many lawsuits name co-respondents, the term is most often thought of in connection with those divorce cases in which adultery is alleged on the part of the defendant. In many these cases, the person with whom the defendant was alleged to have committed adultery was named as the co-respondent. More common in England than in the United States, the practice has fallen into disfavor and is now discouraged.
England's Matrimonial Causes Act 1857 codified the concept of the co-respondent and required that in divorce cases alleging adultery, the person with whom it was committed be named. The co-respondent became a co-defendant, and if the divorce was granted, would usually be required to pay the costs of the divorce and sometimes massive damage payments to the plaintiff. The effect of this system was to shame and humiliate defendants and co-respondents, and also to jeopardize the co-respondents' marriages. It also led to more contested divorces, because co-respondents would sometimes insist on trying to restore their reputations by trying divorce cases which would otherwise have been uncontested.
To be named as the co-respondent in a divorce case was social disaster, especially if married. The popular perception was of a somewhat rakish man, willing to take risks with others' reputations. Often dapper dressers, these weren't stolid married types, at least not while philandering! In fact, the term “co-respondent shoes” became a humorous reference to the type of shoes such men would stereotypically wear, easily memorable with patterns or colors, especially when left outside a hotel room door for shining while the couple stayed behind the locked door.
In the United States, the rules governing marriage and divorce are set by each of the states, and it's not necessary in most states to allege adultery or name a co-respondent when it is claimed. In the United Kingdom, by contrast, the only ground for divorce is “irretrievable breakdown,” which is supported in a divorce petition by presentation and proof of facts, of which adultery is one of only five permissible. In addition, claiming adultery permits an expedited divorce process, which may explain why it's alleged in four of five divorce petitions in the United Kingdom.
As the 20th century drew to a close, more courts in the UK permitted allegations of adultery without naming names; this relaxation of standards, however, was not universal. In the early part of the 21st century, as part of an overall reform of the marriage and divorce laws, British law changed to permit the allegation of adultery without the requirement that a co-respondent be named, although it did not ban the practice altogether. This was seen by most as a positive step because it shifted the focus of a divorce proceeding away from establishing blame. It also reduced the number of contested divorces because co-respondents no longer had to try to restore their reputations.