How do I use the SQL WHERE IN construct with PetaPoco?

This will work except you can’t use the @0 (ordinal) syntax. You must use named parameters, otherwise it thinks they are individual parameters.

var tagsToFind = new string[] { "SqlServer", "IIS" };
var sql = PetaPoco.Sql.Builder.Select("*").From("Tags").Where("Name in (@tags)", new { tags = tagsToFind });
var result = db.Query<Tag>(sql);

This will result in

select * from Tags where name in (@0, @1);
@0 = SqlServer, @1 = IIS