In general, performing unnecessary labor is prohibited during Hol HaMoed, but under certain conditions various tasks are permitted.

It is permitted to perform labor on Hol HaMoed in order to prevent one’s property from being ruined or in order to prevent monetary loss. This category of cases is known as davar ha’aved. An example of this is a merchant who has merchandise in his possession before the festival that will be ruined if he does not sell it during Hol HaMoed. In such cases, it is permitted to engage in labor.

It is permissible to perform labors that are necessary for one’s observance of the festival. This includes food preparation or the attainment of anything one needs for the festival. Similarly, it is permitted to shop on Hol HaMoed for things that one needs for the festival.

If one is in a difficult financial state, such that if he does not work during Hol HaMoed he will be unable to provide the basic festival needs for his family and guests, he may work during the intermediate festival days on condition that he does so as discreetly as possible.

The category of a labor that is performed for the needs of the public includes anything that must be done to satisfy the needs of many people. For example, in an Israeli town where the government is run by Jews, if it becomes necessary to repair torn electrical wires, or simply to remove the garbage, this is considered “for public need” and it is permitted on Hol HaMoed.

Any action that does not involve much effort, i.e., which does not take long and does not require any special exertion or concentration, is permitted on Hol HaMoed, even if it is defined as a labor according to the halakhot of Shabbat and festivals. This category includes lighting a fire, driving a car, using the telephone, turning on an electrical appliance, or carrying objects from one domain to another. By contrast, actions that are not defined as prohibited labor on Shabbat and festival days but which involve great effort, e.g., carrying heavy objects from one corner of a room to another, are prohibited on Hol HaMoed if they are not necessary.

In addition to all of the above, one must be careful with regard to the appearance of transgression in the case of work on Hol HaMoed. For an explanation of this concept, see the chapter “The Appearance of Transgression” in the halakhot of Shabbat (p. 454).

It is permitted to talk about business matters during Hol HaMoed.