Carl Johannes With (December 11, 1877 – June 16, 1923) was a Danish doctor and arachnologist, specialising in pseudoscorpions and mites.With was born in Lemvig to Nicolai Rasmus With and his wife Rasmine Sophie Dorothea With, but was orphaned by the age of five.
With married Inge Kiørboe on July 1, 1909, and together they had three children.
With died in 1923 in Skibstrup, in the parish of Hellebæk (Helsingør Municipality), while still working on a dissertation on lupus.