AutoMapper convert from multiple sources

You could use a Tuple for this:

Mapper.CreateMap<Tuple<People, Phone>, PeoplePhoneDto>()
    .ForMember(d => d.FirstName, opt => opt.MapFrom(s => s.Item1.FirstName))
    .ForMember(d => d.LastName, opt => opt.MapFrom(s => s.Item1.LastName))
    .ForMember(d => d.Number, opt => opt.MapFrom(s => s.Item2.Number ));

In case you would have more source models you can use a different representation (List, Dictionary or something else) that will gather all these models together as a source.

The above code should preferaby be placed in some AutoMapperConfiguration file, set once and globally and then used when applicable.

AutoMapper by default supports only a single data source. So there is no possibility to set directly multiple sources (without wrapping it up in a collection) because then how would we know what in case if for example two source models have properties with the same names?

There is though some workaround to achieve this:

public static class EntityMapper
{
    public static T Map<T>(params object[] sources) where T : class
    {
        if (!sources.Any())
        {
            return default(T);
        }

        var initialSource = sources[0];

        var mappingResult = Map<T>(initialSource);

        // Now map the remaining source objects
        if (sources.Count() > 1)
        {
            Map(mappingResult, sources.Skip(1).ToArray());
        }

        return mappingResult;
    }

    private static void Map(object destination, params object[] sources)
    {
        if (!sources.Any())
        {
            return;
        }

        var destinationType = destination.GetType();

        foreach (var source in sources)
        {
            var sourceType = source.GetType();
            Mapper.Map(source, destination, sourceType, destinationType);
        }
    }

    private static T Map<T>(object source) where T : class
    {
        var destinationType = typeof(T);
        var sourceType = source.GetType();

        var mappingResult = Mapper.Map(source, sourceType, destinationType);

        return mappingResult as T;
    }
}

And then:

var peoplePhoneDto = EntityMapper.Map<PeoplePhoneDto>(people, phone);

But to be quite honest, even though I am using AutoMapper for already a few years I have never had a need to use mapping from multiple sources. In cases when for example I needed multiple business models in my single view model I simply embedded these models within the view model class.

So in your case it would look like this:

public class PeoplePhoneDto {
    public People People { get; set; }
    public Phone Phone { get; set; }
}

You cannot directly map many sources to single destination - you should apply maps one by one, as described in Andrew Whitaker answer. So, you have to define all mappings:

Mapper.CreateMap<People, PeoplePhoneDto>();
Mapper.CreateMap<Phone, PeoplePhoneDto>()
        .ForMember(d => d.PhoneNumber, a => a.MapFrom(s => s.Number));

Then create destination object by any of these mappings, and apply other mappings to created object. And this step can be simplified with very simple extension method:

public static TDestination Map<TSource, TDestination>(
    this TDestination destination, TSource source)
{
    return Mapper.Map(source, destination);
}

Usage is very simple:

var dto = Mapper.Map<PeoplePhoneDto>(people)
                .Map(phone);