diff --git a/_episodes/19-custom-types.md b/_episodes/19-custom-types.md
new file mode 100644
index 00000000..39fe3757
--- /dev/null
+++ b/_episodes/19-custom-types.md
@@ -0,0 +1,92 @@
+---
+title: "Custom Types"
+teaching: 10
+exercises: 0
+questions:
+- "How do I create and import my own custom types into a CWL description?"
+objectives:
+- "Learn how to write custom CWL object types."
+- "Learn how to import these custom objects into a tool description."
+keypoints:
+- "You can create your own custom types to load into descriptions."
+- "These custom types allow the user to configure the behaviour of a tool
+   without tinkering directly with the tool description."
+- "Custom types are described in separate YAML files and imported as needed."
+---
+
+Sometimes you may want to write your own custom types for use and reuse in CWL
+descriptions. Use of such custom types can reduce redundancy between multiple
+descriptions that all use the same type, and also allow for additional
+customisation/configuration of a tool/analysis without the need to fiddle with
+the CWL description directly.
+
+The example below is a CWL description of the [InterProScan][ips] tool for
+simultaneously searching protein sequences against a wide variety of resources.
+It is a good example of a number of good practices in CWL.
+
+*custom-types.cwl*
+
+~~~
+{% include cwl/custom-types.cwl %}
+~~~
+{: .source}
+
+*custom-types.yml*
+
+~~~
+{% include cwl/custom-types.yml %}
+~~~
+{: .source}
+
+On line 34, in `inputs:applications`, a list of applications to be used in the
+search are imported as a custom object:
+
+```
+inputs:
+  proteinFile:
+    type: File
+    inputBinding:
+      prefix: --input
+  applications:
+    type: InterProScan-apps.yml#apps[]?
+    inputBinding:
+      itemSeparator: ','
+      prefix: --applications
+```
+{: .source}
+
+The reference to a custom type is a combination of the name of the file in which
+the object is defined (`InterProScan-apps.yml`) and the name of the object
+within that file (`apps`) that defines the custom type. The square brackets `[]`
+mean that an array of the preceding type is expected, in this case the `apps`
+type from the imported `InterProScan-apps.yaml` file
+
+The contents of the YAML file describing the custom type are given below:
+
+~~~
+{% include cwl/InterProScan-apps.yml %}
+~~~
+{: .source}
+
+In order for the custom type to be used in the CWL description, it must be
+imported. Imports are described in `requirements:SchemaDefRequirement`, as
+below in the example `custom-types.cwl` description:
+
+```
+requirements:
+  ResourceRequirement:
+    ramMin: 10240
+    coresMin: 3
+  SchemaDefRequirement:
+    types:
+      - $import: InterProScan-apps.yml
+```
+{: .source}
+
+Note also that the author of this CWL description has also included
+`ResourceRequirement`s, specifying the minimum amount of RAM and number of cores
+required for the tool to run successfully, as well as details of the version of
+the software that the description was written for and other useful metadata.
+These features are discussed further in other chapters of this user guide.
+
+[ips]: https://github.com/ebi-pf-team/interproscan
diff --git a/_includes/cwl/InterProScan-apps.yml b/_includes/cwl/InterProScan-apps.yml
new file mode 100644
index 00000000..e42779c3
--- /dev/null
+++ b/_includes/cwl/InterProScan-apps.yml
@@ -0,0 +1,18 @@
+type: enum
+name: apps
+symbols:
+ - TIGRFAM
+ - SFLD
+ - SUPERFAMILY
+ - Gene3D
+ - Hamap
+ - Coils
+ - ProSiteProfiles
+ - SMART
+ - CDD
+ - PRINTS
+ - PIRSF
+ - ProSitePatterns
+ - Pfam
+ - ProDom
+ - MobiDBLite
diff --git a/_includes/cwl/custom-types.cwl b/_includes/cwl/custom-types.cwl
new file mode 100644
index 00000000..75d1b294
--- /dev/null
+++ b/_includes/cwl/custom-types.cwl
@@ -0,0 +1,67 @@
+cwlVersion: v1.0
+class: CommandLineTool
+
+label: "InterProScan: protein sequence classifier"
+
+doc: |
+      Version 5.21-60 can be downloaded here:
+      https://github.com/ebi-pf-team/interproscan/wiki/HowToDownload
+
+      Documentation on how to run InterProScan 5 can be found here:
+      https://github.com/ebi-pf-team/interproscan/wiki/HowToRun
+
+requirements:
+  ResourceRequirement:
+    ramMin: 10240
+    coresMin: 3
+  SchemaDefRequirement:
+    types:
+      - $import: InterProScan-apps.yml
+
+hints:
+  SoftwareRequirement:
+    packages:
+      interproscan:
+        specs: [ "https://identifiers.org/rrid/RRID:SCR_005829" ]
+        version: [ "5.21-60" ]
+
+inputs:
+  proteinFile:
+    type: File
+    inputBinding:
+      prefix: --input
+  applications:
+    type: InterProScan-apps.yml#apps[]?
+    inputBinding:
+      itemSeparator: ','
+      prefix: --applications
+
+baseCommand: interproscan.sh
+
+arguments:
+ - valueFrom: $(inputs.proteinFile.nameroot).i5_annotations
+   prefix: --outfile
+ - valueFrom: TSV
+   prefix: --formats
+ - --disable-precalc
+ - --goterms
+ - --pathways
+ - valueFrom: $(runtime.tmpdir)
+   prefix: --tempdir
+
+
+outputs:
+  i5Annotations:
+    type: File
+    format: iana:text/tab-separated-values
+    outputBinding:
+      glob: $(inputs.proteinFile.nameroot).i5_annotations
+
+$namespaces:
+ iana: https://www.iana.org/assignments/media-types/
+ s: http://schema.org/
+$schemas:
+ - https://schema.org/docs/schema_org_rdfa.html
+
+s:license: "https://www.apache.org/licenses/LICENSE-2.0"
+s:copyrightHolder: "EMBL - European Bioinformatics Institute"
diff --git a/_includes/cwl/custom-types.yml b/_includes/cwl/custom-types.yml
new file mode 100644
index 00000000..ec8fb9e6
--- /dev/null
+++ b/_includes/cwl/custom-types.yml
@@ -0,0 +1,3 @@
+proteinFile:
+    class: File
+    path: test_proteins.fasta
diff --git a/_includes/cwl/test_proteins.fasta b/_includes/cwl/test_proteins.fasta
new file mode 100644
index 00000000..ec34ed42
--- /dev/null
+++ b/_includes/cwl/test_proteins.fasta
@@ -0,0 +1,34 @@
+>Q97R95
+MKYKRIVFKVGTSSLTNEDGSLSRSKVKDITQQLAMLHEAGHELILVSSGAIAAGFGALG
+FKKRPTKIADKQASAAVGQGLLLEEYTTNLLLRQIVSAQILLTQDDFVDKRRYKNAHQAL
+SVLLNRGAIPIINENDSVVIDELKVGDNDTLSAQVAAMVQADLLVFLTDVDGLYTGNPNS
+DPRAKRLERIETINREIIDMAGGAGSSNGTGGMLTKIKAATIATESGVPVYICSSLKSDS
+MIEAAEETEDGSYFVAQEKGLRTQKQWLAFYAQSQGSIWVDKGAAEALSQYGKSLLLSGI
+VEAEGVFSYGDIVTVFDKESGKSLGKGRVQFGASALEDMLRSQKAKGVLIYRDDWISITP
+EIQLLFTEF
+>A2VDN9
+MEVKGKKKLTGKGTKMSQEKSKFHKNNDSGSSKTFPKKVVKEGGPKITSKNFEKTATKPGKKGVKQFKNKQQGDRIPKNK
+FQQANKFNQKRKFQPDSKSDESAAKKPKWDEFKKKKKELKQSRQLSDKTNYDIVIRAKQIWEILRRKDCDKEKRVKLMSD
+LQKLIQGKIKTIAFAHDSTRVIQCYIQFGNEEQRKQAFEELRGDLVELSKAKYSRNIVKKFLMYGSKAQIAEIIRSFKGH
+VRKLLRHAEASAIVEYAYNDKAILEQRNMLTEELYGNTFQLYKSADHPTLDKVLEVQPEKLELIMDEMKQILTPMAQKEA
+VIKHSLVHKVFLDFFTYAPPKLRSEMIEAIREAVVYLAHTHDGARVAMYCLWHGTPKDRKVIVKTMKTYIEKVANGQYSH
+LVLLAAFDCIDDTKLVKQIIISEIINSLPNIVNDKYGRKVLLYLLSPRDPAHTVREIIEVLQKGDGNAHSKKDTEIRRRE
+LLESISPALLSYLQGHAQEVVLDKSACVLVADILGTATGDVQPAMDAVASLAAAELHPGGKDGELHIAEHPAGHLVLKWL
+IEQDKKMKERGREGCFAKTLIERVGVKNLKSWASVNRGAIILSSLLQSSDQEVANKVKAGLKSLIPALEKSKNTSKGIEM
+LLEKLTA
+>A2YIW7
+MAAEEGVVIACHNKDEFDAQMTKAKEAGKVVIIDFTASWCGPCRFIAPVFAEYAKKFPGAVFLKVDVDELKEVAEKYNVE
+AMPTFLFIKDGAEADKVVGARKDDLQNTIVKHVGATAASASA
+>P22298
+GRGLLPFVLLALGIXAPWAVEGAENALKGGACPPRKIVQCLRYEKPKCTSDWQCPDKKKC
+CRDTCAIKCLNPVAITNPVKVKPGKCPVVYGQCMMLNPPNHCKTDSQCLGDLKCCKSMCG
+KVCLTPVKA
+>A0B6J9
+MSKIGKSIRLERIIDRKTRKTVIVPMDHGLTVGPIPGLIDLAAAVDKVAEGGANAVLGHM
+GLPLYGHRGYGKDVGLIIHLSASTSLGPDANHKVLVTRVEDAIRVGADGVSIHVNVGAED
+EAEMLRDLGMVARRCDLWGMPLLAMMYPRGAKVRSEHSVEYVKHAARVGAELGVDIVKTN
+YTGSPETFREVVRGCPAPVVIAGGPKMDTEADLLQMVYDAMQAGAAGISIGRNIFQAENP
+TLLTRKLSKIVHEGYTPEEAARLKL
+>P02939
+MNRTKLVLGAVILGSTLLAGCSSNAKIDQLSTDVQTLNAKVDQLSNDVTAIRSDVQAAKD
+DAARANQRLDNQAHSYRK
\ No newline at end of file